Numerous fixes, including:

* The list of topics can now be be viewed without a timeout
* Languages can be edited
* Outgoing email domains can be configured
* Removing pointless rails_admin relations to speed up and improve the admin
  experience
* Entities can be edited through rails_admin.

This will resolve several redmine issues, but before editing is truly useful
we'll need to default all columns to empty strings, see Redmine #8087