Fixes to notifications

## Tasks

### Bugs
- [x] Participant status switched to approved, declined, revoked or reinstated by organizer, the message is sent to organizer and NOT participant! **This seems like it was working?? Let me know if it's still broken**
- [x] In registration requested mode the owner of challenge gets wrong kind of notification. "The user _____ was accepted into your competition" the right message would be "The registration of user ___ is pending, please go to ____right url to accept/reject their application"
- [x] Email has http://www.codalab.org not codalabtest.cloudapp.net
- [x] Fix missing names

### Change confusing wording

- [x] When privileges are revoked we get: “Your status has been revoked.” Change to: “Your participation privileges have been suspended”.
- [x] When re-instated we get: "Your status has been accepted!" we should get "Your participation privileges have been restored”. **This would require adding some more logic that I feel isn't worth putting off higher priority features for. If you'd like please make a new issue and we'll prioritize it accordingly!**
- [x] When denying a participant access to the competition (not revoking, first time denying), the message to the organizer is  “The user madclam was revoked permission from your competition:” A more accurate message would be:
“The user madclam was denied permission from your competition:”
- [x] when a participant is revoked, the message he gets is: "Your request to participate in this competition was denied.” instead of  “Your participation privileges have been suspended”.