Moderator ui

The basic functionality for the admin page is done, but the implementation might not be optimal.
Currently you don't immediately see a new added owner/moderator, if you add them after selecting a queue with no previous users in that list.
The layout can also be improved. The 'Admin' menu option is now displayed if you are owner of any queues, even if you are not admin (since the page for queue management is shared).

Creating this PR for feedback.