Add basic group detail page

The rough layout was inspired by the wireframes.
Add a form to edit group settings

I followed an often used convention of using /model/{id}/edit/ as the
url for displaying the form. The form POSTs back to /model/{id}/edit/
and then redirects to /model/{id}/ on success.
Set default RDS PostgresSQL version to 9.3.5

This version is the first version to support read-only replicas with
RDS.
Add title field to Event, automatically generate slug

Changed url_name to slug for consistency with Group

Uses the shortuuid library to generate unique 21 character slugs for
private events.
(https://github.com/stochastic-technologies/shortuuid)
Fix typo
Allow overriding of default Django registration templates

The Django Admin site is before Django registration in the INSTALLED_APPS
list.  Rather than mucking with the INSTALLED_APPS order (which seemed to
have no affect anyways), it seems cleaner to use the filesystem template
loader to pick up these templates
Fix Django Debug toolbar

With nginx in place the REMOTE_ADDR field in the HTTP header is no longer
10.0.2.2, but instead 127.0.0.1
Add some empty templates for use as prototypes

Also cleans up some urls/views:
 - 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
Initial styling
Remove .DS_Store files and add to gitignore