Improve how File Lock feature works with nested items
related https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/440
We discussed it with @DouweM and the plan is:
- Show the tooltip like this “Valery locked
lib/some_file.rb10 minutes ago” (or “this file”) or “Valery lockedlib/10 minutes ago". So we should show lock state by every item in tree.