Events sent to controllers can bubble

If you return true from an event handler on a controller, it
will continue to bubble (presumably to the router).

This is part of `routeTo` work:
https://github.com/emberjs/ember.js/pull/2522

Also related, on the router.js side:
https://github.com/tildeio/router.js/pull/15
Merge pull request #2577 from machty/bubbling-controller-events

Events sent to controllers can bubble