Initial templates for "huh" pages
Learn how to use {% url %} ;)
Finally, after nearly a year, explain what it is that we do.

Fixes Inboxen/infrastructure#7
Add join button to "huh?" page
Centre Join button on huh page
Add LoginRequiredMixin where required
Fix import error
MJMS Proof Reading Services suggested these changes
Minor typoes and cleanups
Fix deleting of emails from inbox view and make delete a form button not an anchor (more http friendly)