Fixes to notifications

## Tasks

- [ ] Participant status switched to approved, declined, revoked or reinstated by organizer, the message is sent to organizer and NOT participant!
- [ ] 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"
- [ ] Email has http://www.codalab.org not codalabtest.cloudapp.net

- Change confusing wording
- [ ] When privileges are revoked we get: “Your status has been revoked.” Change to: “Your participation privileges have been suspended”.
- [ ] When re-instated we get: "Your status has been accepted!" we should get "Your participation privileges have been restored”.
- [ ] 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access to the competition (not revoking, first time denying), the message to the organizer is  “The user madclam was revoked permission from your competition:” A more accurate message would be: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:”
- [ ] 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”.