Add more tests for BigbluebuttonCustomRoomsController#check_user_limit

refs #1385
Fix ExceptionNotification after migration to 4.0.x (for Rails 4)

The way it is configured changed a lot, had to create the initializers again.
It also works for exceptions thrown in resque jobs :gem:

Added tests for the rescue_from blocks in ApplicationController.
Update bigbluebutton_rails, fix one of its resque tasks