Add a new Recent section in the board switcher along with a
All section which like old times display all the available boards.
Recent section lists the recent 5 boards you have visited for a quick
switch.

We needed to disable a few eslint-config-airbnb-base rules in order
to keep the number of line changes under control.  These should be
re-enabled asap.

Rename btn-new, btn-create and btn-save to btn-success
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Partially addresses #47006.

Reduced the technical debt around our JS flash function by making it a
module that is imported rather than relying on the global function.
The global function still exists mainly for technical debt with how
some requests are being completed, but new JS should import the module
directly.

Also reduces some tech debt in the file by removing the need for jQuery.
Instead Flash is now 100% vanilla JS.

[ci skip]

added key to assignee avatar loop

Backport Fix locked milestone in boards being remove-able.
See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1963

Fix https://gitlab.com/gitlab-org/gitlab-ee/issues/2433

Conflicts:
	app/assets/javascripts/boards/boards_bundle.js
	app/assets/javascripts/boards/filtered_search_boards.js
	app/assets/javascripts/filtered_search/filtered_search_manager.js
	spec/features/boards/boards_spec.rb