Create separate fragments for creating and updating events

The fragment class hierarchy:

                   EditEventFragment
                   (generic editing)
                           |
           +---------------+---------------+
           |                               |
   CreateEventFragment            UpdateEventFragment
     (new event)                    (existing event)

Activity hierarchy:

                NewEventActivity
          (contains CreateEventFragment)
                        |
                        |
                EditEventActivity
          (contains UpdateEventFragment)
URLs in alphabetical order in pagerslidingtabstrip xml
Clean up unused imports
Move AttendanceStatus to models package