Use outer join for issues ordering by milestones due.

This MR contains an implementation for Solution 1 suggested in #14183 

Ordering by Milestone due sooner/later ("milestone sort") filters issues without a milestone, which can let users feel like disappearing issues without a milestone.

See merge request !3872

Update annotations on models



See merge request !3962

Assign labels milestone when moving issue

Closes #14532.

See merge request !3934

Add note to requirements doc on swap recommendation, and ensuring enough available memory.

Called out as a result of 2GB RAM DO droplets not being enough to run backups on without adding a swap file. See: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1267

cc\ @stanhu @axil 

See merge request !4060

clarify changelog entry on GitHub Enterprise import support

/cc @stanhu 

See merge request !4066

[ci skip]

Rake drop tables with cascade

See merge request !4020

Fix importer bug when throwing exceptions

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/15681

See merge request !3941

Add a note to testing docs about the `:each` argument to RSpec hooks

[ci skip]

See merge request !4061

[ci skip]

Use tag_exists? in GitAccess#protected_tag?

This will fail until https://gitlab.com/gitlab-org/gitlab_git/merge_requests/81/ is merged. Adding this should speed up checking for tags in `Gitlab::GitAccess` as it no longer needs to retrieve the entire list of tags.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/14280 for more information.

See merge request !3983

Previously this method would directly receive the output of tag_name().
This method could either return a String or nil. In the previous setup
this would somehow magically work but because Rugged::TagCollection#[]
doesn't accept nil values it started to fail.

To work around this the elsif in change_access_check() assigns the
result of tag_name() to a local and then _only_ calls protected_tag?()
if the tag name is not nil. The extra parenthesis are put in place to
ensure that things are parsed correctly, without these the code would be
parsed as follows:

    elsif tag_ref = (tag_name(ref) && protected_tag(tag_ref))

During runtime this would basically resolve to:

    elsif tag_ref = (tag_name(ref) && protected_tag(nil))

This is because when you refer to the variable you're assigning _in_ the
assignment Ruby returns nil instead of raising an error.

This removes the need for retrieving the entire list of tags just to
check if a specific one exists.

Moved entry for !3880 to 8.7.2

See merge request !4058

Apparently this was already released in 8.7.2 but no changelog entry was
added.

[ci skip]

Added CHANGELOG entries for !3880 and !3931

See merge request !4057

[ci skip]

[ci skip]

Upgrade Sidekiq to 4.1.2

Fixes a memory leak: https://github.com/mperham/sidekiq/commit/a2bdb875fe495bc28b1bee80120e4a5641ca0731

See merge request !4056

Fix the line code when importing PR review comments from GitHub

Pull Request Review Comments are comments on a portion of the unified diff.

Closes #17205

See merge request !4010

Pull Request Review Comments are comments on a portion of the unified
diff.

15179 builds page redesign

Closes #15179   

<img src="/uploads/d9ec515e500dc9023d588b5c38636a86/Screen_Shot_2016-04-26_at_1.35.11_PM.png" width="800px">

Updated screenshot:   
<img src="/uploads/63109057ee271d788ab726e52acf9328/Screen_Shot_2016-05-04_at_9.23.01_AM.png" width="800px">

Updated screenshot with count badges instead of parentheses:  
<img src="/uploads/d9cd91b079d23c63601c8dbcf4803c8d/Screen_Shot_2016-05-05_at_7.40.48_AM.png" width="800px">

See merge request !3935

Moved TeamCity changelog entry to 8.7.3

See merge request !4049

[ci skip]

Merge branch 'master' of gitlab.com:gitlab-org/gitlab-ce into issue_14532_assign_labels_milestone_when_moving_issue

Log to application.log when an admin starts and stops impersonating a user

Closes gitlab-org/gitlab-ee#536

See merge request !4028

Use new build badge URLs

Use new build badge URLs to follow the instruction at [the project badges](https://gitlab.com/gitlab-org/gitlab-ce/badges).

See merge request !4037

Merge request widget displays TeamCity build state and code coverage correctly again

## What does this MR do?
This MR contains a fix for a regression introduced in `8.7`. In former version, the TeamCity build status was always displayed correctly. In `8.7` the build state is still checked, but the UI is not updated correctly any longer.

## Are there points in the code the reviewer needs to double check?
The changes are quite simple, so please simply double check them.

## Why was this MR needed?
This MR is needed to make the TeamCity build status working again.

## What are the relevant issue numbers?
#17080 

See merge request !3998

Use `number_to_human_size` helper to show repository size

This will intelligently format large repository sizes in GBs (or,
shudder, TBs).

Also, removes `rescue` clause from `repository_size` helper.
The repository size has since become calculated (and cached)
more intelligently, and this should no longer be necessary.

See merge request !4047