Expand Admin UI

* Add management of BatchJob and JobQueue to admin interface
** This is a partial solution to #10
* Remove new, create and destroy actions from Work admin interface
* Add extra filters and columns to Work admin interface
* Update BatchJob model so dependent records (JobQueue, PageResult, PostprocPage) are destroyed when the associated BatchJob is destroyed
* Add name virtual attribute to Font model which helps ActiveAdmin correctly assign labels in the interface