Merge branch 'admin-cleanup'

Merge branch 'admin-cleanup'

* admin-cleanup:
  Making Attribute and Relationship inlines collapsible with custom template.
  Hiding save_on_top on the Page add form template, and adding template documentation to Page change forms when the page's selected template provides it.
  Pages now have a custom add form template which notifies the user that they must select a template and save before containers will be available.
  Implementing NodeAdmin and subclasses for built-in Node types.