Fixed issue with tasklist toggling sidebar refresh

Closes #15270

See merge request !3782

Added loading icon to import buttons

See #14488 for more details

See merge request !3662

Print style

[test.pdf](/uploads/0dab5c1b2d0c4d0cd7e8930e9b660a9f/test.pdf)

Closes #14201

See merge request !3784

Discussion notes update

- At the moment discussion notes are rendered in a list but arent actually a list item and that can cause overflow issues
- Moved the dates to be in the header like other notes
- Fixed overlapping issue on mobile

See merge request !3720

Add environment variables on a job level in CI

Make it possible to define environment variables on a job level.

Closes #14716

See merge request !3612

Scroll to the last comment I made and edit it.

Pressing up in an empty comment box will edit your last comment. 

Also now when you click edit on a comment it will put the cursor at the end.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15267

![scrollup](/uploads/b056fdc479d39311f2be412458028a83/scrollup.gif)

See merge request !3757

At this point this is being handled by GitLab Runner and we need to
introduce this as a separate merge request.

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

Closes #14201

Use Module#prepend for method instrumentation

cc @pcarranza 

See merge request !3754

Closes #15270

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