Upgrade the airbrake gem

* Remove JS notifier from templates and libraries
* Cleanup references to JS notifier in tests
* Merge pull request #297 from airbrake/remove-js-notifier
* Revert "Merge pull request #297 from airbrake/remove-js-notifier"
* Add deprecation warning when using .
* Remove the Airbrake JS notifier for the major release.

https://trello.com/c/KEflOGgR