New diff notes

Fixes #12732, #14731, #19375, #14783 

Builds on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4110

To do:
- [x] Get it mostly working
- [x] Validate position validity
- [x] Fix: Don’t link to `#`
- [x] Fix: Base ref can be `nil`, potentially, when the MR has an oprhan source branch => Yep, doesn’t work. We need to store a `start_id`
- [x] Optimize: Fewer duplicate `git diff` compares
- [x] Optimize: Pass paths to `PositionTracer#diff` for faster diffs
- [x] Refactor: Use `head_id` in `MergeRequest`/`MergeRequestDiff` instead of `source_sha`
- [x] Refactor: Convert existing array-based diff refs to the DiffRefs model
- [x] Tweak: Use `note_type` in `Autosave` key
- [x] Tweak: Remove `line_code: note.line_code` from `link_to_reply_discussion`
- [x] Update: `SentNotifications` and reply-by-email receiver
- [x] Update: MR diff notification email
- [x] Update: API (MR, Commit note creation and entity)
- [x] Update: GitHub importer
- [x] Address any other TODO comments
- [x] Fix: Suppress "edited 4 minutes ago"
- [x] Write tests
  - [x] `LineMapper`
  - [x] `PositionTracer`
  - [x] `Position`
  - [x] `DiffPositionUpdateService`
  - [x] `DiffNote`
  - [x] `MergeRequests::RefreshService` / `MergeRequest#update_diff_notes_positions`
- [x] Make sure commits with diff notes don't get cleaned up, since this would prevent the diff notes from being rendered (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5062)

Future improvements:
- Display unresolved comments on files outside the diff, if the comment was added when that file _was_ part of the diff
- Allow commenting on sections between hunks, when expanding the diff using `...`
  - (We'd need to generate line code based on Position if we have it, even if it falls outside bounds of diff)
- `diff_hunk` on diff note API entity
- Show diff hunk in notification email
- Resolved line notes would have a boolean, and be inactive through `notes.any? { !active? || resolved? }`
- Multi line notes would store a number of positions, and do the right thing (™) in grouping and then rendering if the first item is multiline? => true
- Image diff notes could store x,y,width,height instead of old_line,new_line for similar grouping. Does it need a reference to say if it's on old or new? These can't have line_codes, clearly. Rendering would be interesting.
- Show commit line comments in the MR diff
- Comment on specific selected words
- Comment on file header
- Unfold top of discussion diff note
- New diff notes API for commits and MRs

/cc @rspeicher

See merge request !4101

Exclude projects pending delete from notifications

Make `NotificationSetting.for_projects` exclude projects that are excluded by the default scope on `Project`. (At the moment, that's projects with `pending_delete: true`.)

See https://gitlab.com/gitlab-com/support-forum/issues/819

See merge request !5138

Improve UI consistency for admin area

Closes #3946

See merge request !4424

Remove icons from file edit tabs

We don't need this icons and it also inconsistent with current UI 

See merge request !5072

If the Sidekiq job fails for some reason, a project can be 'stuck'
pending deletion. The project can't be viewed, so it shouldn't be
available through the notification settings association as this will
throw an exception when we try to show the link.

Escape file extension when parsing search results

When a file extension contains characters which have a meaning in regular expressions, the search may crash.

Fixes #18553 

See merge request !5141

Fixes 404 redirect after validation fails importing a project

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19558

See merge request !5143

Fix log statements in import/export

Fixes - as seen in the logs:
```
Import/Export error raised on /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/import_export/file_importer.rb:19:in `rescue in import': undefined method `message' for #<String:0x007fc45e977e10>
```

See merge request !5129

Add information when member joined a team

## What does this MR do?
It adds timeago label by every member on team page
## Are there points in the code the reviewer needs to double check?

Yes, maybe design is not OK, please check.

## Why was this MR needed?

It's useful information

## What are the relevant issue numbers?

## Screenshots (if relevant)

![joxi_screenshot_1467820915126](/uploads/9e5657443a10a9fe204367d7b6749b1f/joxi_screenshot_1467820915126.png)



See merge request !5116

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

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

Services: code style fixes, minor refactoring

## What does this MR do?

It contains code style fixes, minor refactoring and also it removes some unnecessary comments. Every comment require a support just like a regular code line and this is why we should avoid using comments everywhere unless it's really helpful. Martin Fowler said "Find comment and refactor the code around it" :) our code is not that bad so let's not spoil it with comments.

## Why was this MR needed?

Because GitLab is a live example of awesome code. Let's keep up a good job :) 


See merge request !5112

Show last push widget in upstream after push to fork

## What does this MR do?

Show the last push widget in the upstream project when you push to a fork. 

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

In the view, I'm checking if `@project` in the first part of the conditional. I felt it was necessary in case `@project` wasn't an object in all cases. Will it ever not be there? Is this check necessary?

Should there be tests? I don't see existing ones for this. 

## Why was this MR needed?

I use the fork workflow everywhere and it has annoyed me for some time that the last push widget doesn't show up when viewing the upstream project. I'm almost never viewing the fork in GitLab so I want to be able to easily create a MR in any case. 

## Screenshots (if relevant)

**Widget in upstream repo:**

![Screen_Shot_2016-06-23_at_10.05.29_AM](/uploads/f823642e40cf059c3793db6cf00bba50/Screen_Shot_2016-06-23_at_10.05.29_AM.png)

**Widget in fork**:

![Screen_Shot_2016-06-23_at_10.05.25_AM](/uploads/1a976241186ec42cdc43c80bea0c856b/Screen_Shot_2016-06-23_at_10.05.25_AM.png)

**Widget on dashboard**:

![Screen_Shot_2016-06-23_at_10.06.07_AM](/uploads/084ac35f67735aec8042d9bc904255fe/Screen_Shot_2016-06-23_at_10.06.07_AM.png)


See merge request !4880

Allow everyone to order tags, not only those who has access

## What does this MR do?
Allows everyone to view tags by different order (by name, date, etc), not only those who has access

## Are there points in the code the reviewer needs to double check?
Just check how it's rendered.

## Why was this MR needed?
Because now I can't order other's project tags.

## What are the relevant issue numbers?
#15438

## Screenshots (if relevant)
Exist in related issue. Look [one comment](https://gitlab.com/gitlab-org/gitlab-ce/issues/15438#note_12888763) and [just below there is another one](https://gitlab.com/gitlab-org/gitlab-ce/issues/15438#note_12888819).

## Does this MR meet the acceptance criteria?
Probably, no need

See merge request !5105