Add new event page

Quite a bit going on here:

 - Adds the basic add event views (except for location)
 - Adds Django-floppyforms for HTML input attributes, like `required`, `type="date"` and `type="time"`
 - Adds a `settings.js` template to allow us to share dynamic data with client-side JS
 - Brings in the Modernizr and Bootstrap-datetimepicker libraries for date/time pickers on unsupported browsers
 - Adds validation to event form for start and end time
The "New Event" link is on the Group edit page, along with (eventually) a list of event, which is why I had it redirect there.  It couldn't hurt to double check on that with @jfrankl or @dboyer once we actually have an Event Detail