Built-in RSVP system.
Add indexes to RSVPs table.
Make RSVP routes more restful. (See details.)

- Also refactored how destroys will happen. (Using .destroy_all instead of
a loop.)
- Also used POST/DELETE verbs instead of GET for RSVP routes.
- Also split RSVPs out of Events controller.
Change RSVP button for non-authed users.
Merge pull request #47 from ckrailo/rsvp

Built-in RSVP system.