Namespace license checks for issue boards with milestones

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/2335

Issue boards with milestones (EES / Bronze)

1. Do not show ability to associate board with a milestone

Introduced in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1150 by @dbalexandre and @iamphill

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/2567

mentioned in issue #2335 (closed)

assigned to @reprazent

mentioned in merge request !2315 (merged)

closed via commit ddd47d9e

closed via merge request !2315 (merged)