Merge branches 'feature/project-export' and 'master' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export

Improve SVG sanitizer to handle namespaced attributes

* Small refactor in the SVG sanitizer
* Enable already whitelisted namespaced attributes to be allowed
* Disable `xlink:href`to reference any external resource

Fixes #18100 

See merge request !4427

Fix Error 500 when using closes_issues API with an external issue tracker

Closes #18484

See merge request !4608

Closes #18484

Improvements to offscreen navigation

Improvements on top of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4579 based on mockups from https://gitlab.com/gitlab-org/gitlab-ce/issues/18417#note_12389766

See merge request !4607

Resolve "Hide Left sidebar paradigm"

## What does this MR do?
Hides the nav bar by default & centers the tanuki logo in the top nav

## Why was this MR needed?
UX

## What are the relevant issue numbers?
Closes #18417 

## Screenshots (if relevant)
![Screen_Shot_2016-06-10_at_12.49.10_PM](/uploads/c281e4c9de1c1bc9af59ebfa8d2bd18b/Screen_Shot_2016-06-10_at_12.49.10_PM.png)
![Screen_Shot_2016-06-10_at_12.49.27_PM](/uploads/635e0a88230105faa5527f6632899ddb/Screen_Shot_2016-06-10_at_12.49.27_PM.png)
<img src="/uploads/3001a9c723037012f1b86cfacfb1225e/Screen_Shot_2016-06-10_at_12.51.41_PM.png" width="500px">

See merge request !4579

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixed search form padding

## What does this MR do?

Corrects the padding of the search form.

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

Ney.

## Why was this MR needed?

UX

## What are the relevant issue numbers?

Closes #18463.

## Screenshots (if relevant)

![Screen_Shot_2016-06-10_at_14.07.32](/uploads/e4d127c66cf7fa3286279367d6e4ea7c/Screen_Shot_2016-06-10_at_14.07.32.png)

## Does this MR meet the acceptance criteria?

- [ ] [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
- [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 !4591

Only create the backup directory if it is local

Closes #12710

See merge request !4551

Closes #12710

Add Project.where_paths_in

In https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4410 I'm working on reducing the SQL queries needed to render Markdown. One reason for the large amount of queries is executing a large number of queries needed to find projects and related data. Basically `Project.find_with_namespace` is called in a loop and then any relations have to be retrieved separately.

By using `Project.where_paths_in` we can work around this by doing something like:

```ruby
project_paths = [...] # populated by some method
projects = Project.where_paths_in(project_paths).includes(:namespace, ...)
```

Ref: https://gitlab.com/gitlab-org/gitlab-ce/issues/18042

See merge request !4535

Changelog fix for search dropdown arrow keys fix

[ci skip]

See merge request !4580

Remove unused MergeRequest#gitlab_merge_status method

Closes #18462.

See merge request !4593

Revert side nav to full width; remove border under nav; remove tooltips on nav links; stop page content shifting with side nav; put project nav in container

Move Labels and Milestones as sub tab to Issues/MR

## What does this MR do?

UI/UX change. Moves project labels and milestone tabs under Issues and Merge request tabs. 

## Why was this MR needed?

To solve problem of having to many tabs in top navigation. Since Labels and Milestones depends on Issue/MR feature it belongs to it and can be removed from top nav.

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18368

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md) - not needed
- [x] API support added - not needed
- [x] Tests
  - [x] Added for this feature/bug - changed existing tests to match new behaviour
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)

cc @jschatz1 @annabeldunstone @skyruler

See merge request !4592

Signed-off-by: Rémy Coutable <remy@rymai.me>

Add workhorse controller and API helpers

Adds `send_git_blob` and `send_git_archive` controller and API helpers to reduce duplication and make Workhorse easier for a developer to work with.

See merge request !4486

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>