Implement an edit queue

A user will be presented with a queue of images, that need editing,
because they either have no tags or no name.
Add tag searching and nicer editing with select2

Tags can be queried via a new API endpoint "/api/tags?q=asdf". This is
used by select2, which also gives nicer editing of tags at the same
time, to make suggestions for existing tags based on the user input.

Currently only 15 matching tags are retrieved to avoid cluttering and
traffic and a minimum of 3 characters has to be entered for a search to
happen.