[FEATURE classname-can-disable-handlers] Optional setup at the EventDispatcher

EventDispatcher brings an optional `disabledHandlerClassName` property, which gives the ability to stop the event delivery and action trigger on the views with that specific className.

This specific question was posted at [SO](http://stackoverflow.com/questions/23632812/how-tell-ember-do-not-fire-click-event-on-disabled-link?noredirect=1#comment36293044_23632812).