Limit number of project export retries to 3

I think 3 should be a sufficient number of retries - at the moment we were doing 20+

This will only send a maximum of 3 emails if the project export went wrong. Tested - project import is not affected.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18966

See merge request !5267

Fix LFS CI fetch

## What does this MR do?
Fixes LFS fetching for CI objects that were kind of broken.

## Why was this MR needed?
This also refactors LFS tests to be a blackbox tests instead of whitebox tests. Actually testing GrackAuth instead of LFSRouter.

## Related isssues
Resolves: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1199

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5270

Allow a project import URL to be blank to prevent false positives in validation

Projects that happen to have blank import URLs were failing validation, causing project settings not to be saved. Loosen the requirement and don't try to use the import data if the URL isn't present.

Closes #19893

See merge request !5309

Fix not normalized emoji paths

## What does this MR do?
It normalizes emoji names in `api` and `toggle_award`

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?
User was able to store +1 and thumbsup to databse, causing UI inconsistency.

## What are the relevant issue numbers?
Fixes #19104 

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5060

preventing settings from being saved

Resolve "Pipelines view has manual actions"

## What does this MR do?
Removes the deploy button from pipelines

## Why was this MR needed?
The button didn't do anything

## What are the relevant issue numbers?
Closes #19907 

## Screenshots (if relevant)
<img src="/uploads/9488cf238f67463f7dac8f9dbc34f7e1/Screen_Shot_2016-07-16_at_5.52.10_PM.png" width="300px">


See merge request !5299

Fix CI yaml example

## What does this MR do?

Fixes a  typo in a CI yaml example.

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/19888

See merge request !5304

Fix a bug where the project's repository path was returned instead of the wiki path

Closes #19842 

See merge request !5292

Don't fail to highlight when Rouge doesn't have a lexer

Fixes issue introduced by upgrade to Rouge 2.0 (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4691)

See merge request !5291

Don't fail when a LegacyDiffNote didn't store the right diff

Fixes https://sentry.gitlap.com/gitlab/gitlabcom/issues/8865/ and https://sentry.gitlap.com/gitlab/gitlabcom/issues/8754/

See merge request !5287

Revert "Merge branch 'gl-dropdown-issuable-form' into 'master'"

Temporarily fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19884

See merge request !5290

This reverts merge request !4970

Don't fail when Ci::Pipeline doesn't have a project

Fixes https://sentry.gitlap.com/gitlab/gitlabcom/issues/8870/

See merge request !5288

Display tooltip for mentioned users and groups

## What does this MR do?

Display tooltip for mentioned users and groups in Markdown.

## Are there points in the code the reviewer needs to double check?

I don't know.

## Why was this MR needed?

No tooltips were displayed.

## What are the relevant issue numbers?

fixes #17060 

## Screenshots

![user-tooltip](/uploads/501b7d1b2a5e6adcadefbc56b08422ec/user-tooltip.png)

![group-tooltip](/uploads/0152a452f9a1ed9fc86101b242f7e4c2/group-tooltip.png)


See merge request !5261

Upgrade to Rouge 2.0

## What does this MR do?

This MR is a refactor of the HTMLGitlab formatter. The original was copy-pasted from the legacy HTML formatter and adapted to suit our needs. In particular, this MR:

* Strips dead code and unused options
* Factors out the "wrapping" into the places that care about it - Bonzai and the view helpers
* Uses the Rouge 2.0 `token_lines` method to split tokens into lines, removing the custom code we used to do the same
* Uses the now-public `span` method instead of re-implementing it ourselves
* Removes options to not split into lines - the places where this feature wasn't being used are now using the plain `Formatters::HTML` instead of this class

See merge request !4691

Allow U2F devices to be used in Firefox

- Adds U2F support for Firefox
- Improve U2F feature detection logic
- Have authentication flow be closer to the spec (single challenge instead of a challenge for each `signRequest`)

- Closes #17341 
- Related to #15337 

See merge request !5177

Don't ask Heather to review documentation MR's



See merge request !5282

add project name and namespace to filename on project export

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19848

 Export filename now includes project and namespace path

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5268

Fix mentioned users on diff notes

## Summary

`DiffNote`, and `LegacyDiffNote` returns empty array for `mentionable_attrs`, because `mentionable_attrs` is not inheritable by subclasses. The problem can be illustrated with this small sample:

```ruby
module Mentionable
  extend ActiveSupport::Concern

  module ClassMethods
    def attr_mentionable(attr)
      mentionable_attrs << [attr.to_s]
    end

    def mentionable_attrs
      @mentionable_attrs ||= []
    end
  end
end

class A
  include Mentionable

  attr_mentionable :foo
end

class B < A
end

A.mentionable_attrs
=> [["foo", {}]]

B.mentionable_attrs
=> []
```

Possible solution using `cattr_accessor`:

```ruby
module Mentionable
  extend ActiveSupport::Concern

  module ClassMethods
    def attr_mentionable(attr)
      mentionable_attrs << [attr.to_s]
    end
  end

  included do
    cattr_accessor :mentionable_attrs, instance_accessor: false do
      []
    end
  end
end

class A
  include Mentionable

  attr_mentionable :foo
end

class B < A
end

A.mentionable_attrs
=> [["foo"]]

B.mentionable_attrs
=> [["foo"]]

B.mentionable_attrs < [:bar]
=> [["foo"], ["bar"]]

A.mentionable_attrs
=> [["foo"], ["bar"]]
```

`mentionable_attrs` is inheritable by subclasses. If a subclass changes the value then that would also change the value for parent class. Similarly if parent class changes the value then that would change the value of subclasses too.

## What are the relevant issue numbers?

Fixes #19807 

Fixes #18022

/cc @stanhu  @DouweM @rspeicher 

See merge request !5243

Revert "Optimistic locking for Issue and Merge Requests"

The migration to add `lock_version` in !5146 to every issue and merge request takes too long on GitLab.com since it has to add a default value of 0 to every row. Unfortunately, Rails 4.2 doesn't work properly if the value is left as `nil`; anything using optimistic locking cannot be edited. 

This bug was fixed in Rails 5.0 via this commit: https://github.com/rails/rails/commit/13772bfa49325a8dc26410d2dcb555665a320f92. I suggest we revert this change for now, and when we upgrade to Rails 5.0 we can reintroduce this feature.

See merge request !5245

Update rubocop to 0.41.2

Adds a couple of cops to the TODO files, but I wanted [a specific cop](https://github.com/bbatsov/rubocop/pull/3135/files) which just had about 65 offences, so Ill do that later.

See merge request !4999