Bug 1041124 - [Messages][Refactoring] Make use of EventDispatcher in MessageManager. r=julien

can't we set beforeEnter and afterLeave in "report"? I think "group" does not need it, right?
You can keep onDeliverySuccess and onReadSuccess in "report", and do the binding once in beforeEnter ? Or add a "constructor" function in "report" that would be called in Information. (looks more and more like we'd need a real prototype-based inheritance here :) ).

And if we attach the event only when we're in the panel, we don't need to check `if (Navigation.isCurrentPanel('report-view', { id: e.message.id }))` anymore, if I don't miss anything, right?