Add form defaults for historical agent descriptions (closes #272)
Fix reading the content type node, which was completely broken because
the conditional format didn't work. Closes #273.
Merge branch 'fix_273'
Add a new Version model and use it for providing more info about deletions.
 - Added backend method to list versions for items
 - Events which create a version have that version attached
 - Deletion events with a version show name of that item when the
   version prior to deletion is available
Refactoring page headers, breadcrumbs, and the control bar
Merge branch 'master' into merge_guides