All issue boards can now be collapsed via a button, re-ordered by
dragging the header, and the vertical collapsed header style was
reworked.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/61050

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/59895

This reverts merge request !27313

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/59895

Added stylelint to static-analysis
Updated yarn dependencies
CSS Fixes and rule adoptions of stylelint
Added stylelint-scss
Deduplicated yarn.lock to clear dependencies

First round of advanced stylelint rules

Mainly Vendor prefix updates related to flex

Updates to more webkit specific vendor prefixes

Finished all vendor specific fixes

Moved now 4 rules to warning

Fixed the new scss lint problems

More stylelint adaptions after rebase

* dropdown position
* add empty state list overflow
* avoid double scrollbars in project dropdown

This reverts merge request !19250