Add some empty templates for use as prototypes

Also cleans up some urls/views:
 - Cleans up the template inheritance between builtin Django Auth templates and our own registration templates
 - Removed individual mapper page view, this will be on the group settings
 - Added achievement and training pages
 - Moved other instances of group name -> group slug
 - Made all events URLs be under `group/<group_slug>/event/<event_slug>`
   This is needed because `Event.slug` is `unique_together` with `Group.slug`

Also: Fixes the Django Debug Toolbar (again)