Small UI improvements to merge request page
Make gray block under tabs identical height. Also same height have blocks on pages like `Groups` etc. So this improvement is targeted for consistency in UI too
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Fixes internal issues
* https://dev.gitlab.org/gitlab/gitlabhq/issues/2591
* https://dev.gitlab.org/gitlab/gitlabhq/issues/2592
cc @DouweM
See merge request !1759