(Auth) Add isEventMod authorization flag
(UserService) Add property for user's Firebase reference

This way, instead of having to access the user profile data like this (example
shows us grabbing all the user's comments):

    FirebaseIO.child('user_profiles/' + $scope.user.profile.id + '/comments')

We can simply access it like this:

    UserService.ref.child('comments')

Which makes the code much more readable and maintainable.
(rules.json) Fix bug with event rules
(Comments) Add first version of CommentService