Create event/<key>/participants resource.

Added participant view CRUD for all types of participants

Details: 
- Supports pagination. 
- Transactional.
- Organizers can manipulate any list and the limits for the event are not enforced. Limits are only enforced when non-organizers try to add themselves to the registered user list or the wait list.

GET
/event/<key>/participants/ORGANIZER?limit=N
/event/<key>/participants/REGISTERED?limit=N
/event/<key>/participants/WAIT_LISTED?limit=N

POST
/event/<key>/participants/ORGANIZER?user=key
/event/<key>/participants/REGISTERED?user=key
/event/<key>/participants/WAIT_LISTED?user=key

DELETE
/event/<key>/participants?user=key

Param details:
- user defaults to me if not specified
- next url will be available if there are more users. Use the limit to minimize the number of fetches of user objects.