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

Fix typos in CI docs.



See merge request !3709