Ability to create milestone for other projects in group from project milestone page

Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1797#note_2668245

mentioned in merge request !1797 (merged)

Milestone changed to 8.7

Milestone changed to 8.8

Milestone changed to %8.9

Removed ~14281 ~157398 labels

Milestone changed to %8.10

Added ~307502 ~19492 labels

Milestone changed to %Backlog

Status changed to closed

mentioned in merge request !14785