Get rid of replies(annotation) call from the Viewer.

The replies(annotation) call of the viewer.html ng-repeat was called in every $digest cycle yet it only needs to be updated upon annotation creation, reply creation, delete.
Therefore an updateReplies event is introduced which is emitted up in the hieararchy and every annotation updates it's new reply_list property (which as it's namesake suggest keep a list of the annotation's replies)