This reverts commit af5242ecb682189c5d8276e1ab1ffe5ce844f2e5.

The GitLab UI update changed the spinner selector from `spinner` to
`gl-spinner`, so we need to update it, so that our tests won't fail.

add stub to the boardsStore to spy on it and be able to use toHaveBeenCalledWith for the pre-defined labels test

(cherry picked from commit a82e4d57a6fbba840a8a944e372b80866a1e48cc)

(cherry picked from commit 9cd745c65bcb51d615399e82d8b26ef5cce972e1)

(cherry picked from commit 813299edd83ace98256b7fc9302f586f0dc2cabc)

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

Changes migration and all other places the attribute is used

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