N+1 improvements for admin

Added some liberal sprinklings of performance boosts to the admin.  Mostly this is from doing eager loading via extra ``includes``, ``with_translations``, or ``with_translations_for``.  In one case ``Edition#last_author`` this meant converting an inline method to an association so it can be eager-loaded.

In the case of DocumentSeries we got rid of the index view entirely (pagination and filtering / searching would be needed to truly speed it up and that's a lot of work).  Instead it redirects the user to the document series page for their org (or to the list of orgs if they don't have one).