Instrument Repository.clean_old_archives

This is done so we have some metrics for https://gitlab.com/gitlab-org/gitlab-ce/issues/15256.

See merge request !3742

Use Module#prepend for method instrumentation

cc @pcarranza 

See merge request !3754

By using Module#prepend we can define a Module containing all proxy
methods. This removes the need for setting up crazy method alias chains
and in turn prevents us from having to deal with all that madness (e.g.
methods calling each other recursively).

Fixes gitlab-org/gitlab-ce#15281

Don't populate the password field on signup validation errors

- Previously, we were pulling `params[:user][:password]` as the default
  value for the password field. This is incorrect; we should be pulling
  it from `@user.password` or the like.

[Closes #14552]

See merge request !3691

- While signing up.

Fixed issue with dropzone not working on new issuable

Closes #15295

See merge request !3760

Add number sign on external issue reference text

Currently, external issue link is `<a ...>123</a>`. After it will be: `<a ...>#123</a>`.

See merge request !3350

Refactored issue header to work better for mobile

This will also work better for when the title makes the buttons drop down a new line

Closes #14228

See merge request !3487

Make a user available for the user variable

Fixes: #15289 

`current_user` is not available if one is signed out. 

Look for @dzaporozhets's user if available or just user with id `1`. Dz will work on GitLab.com and user with id 1 will work on dev. 

See merge request !3766

This will also work better for when the title makes the buttons drop down a new line

Closes #14228

Put issuable owner and participating people first on mention suggestions

Closes #14423

**Merge Requests**

Author and people who participated are first now


<img src="/uploads/dd75937627c61b5efe631b4a35f274c6/Screen_Shot_2016-03-29_at_6.41.29_PM.png" width="235" />

**Issues**

Author showing first and no people have participated

<img src="/uploads/e17aa96ffe7d46a7dbe293318e999e1d/Screen_Shot_2016-03-29_at_6.41.44_PM.png" width="279" />


See merge request !3448

Add test coverage parsing example for gcvor



See merge request !3629