This reverts commit af5242ecb682189c5d8276e1ab1ffe5ce844f2e5.

This has the benefit that CE bundles will remove dead code in CE only
builds.

We have a follow-up issue to get rid of this completely:

https://gitlab.com/gitlab-org/gitlab-ce/issues/64173

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

Some classes in vue_shared were used only by boards, so they were
moved to the boards directory.

This commit is the result of running `yarn eslint --fix` after enabling
the `no-implicit-coercion` ESLint rule.  This rule has been added to
our ESLint config here:

https://gitlab.com/gitlab-org/gitlab-eslint-config/merge_requests/14

This change brings new Scoped labels to Issue board as well.
With the last change, this was missed.

Scoped labels in EE require additional changes in CE code.

In order to ensure we have the right endpoint to query for an
issue's possible valid labels, we store that url in the issue
object that gets passed to the frontend.