WIP Fix replies toggle visual glitch in edit mode

This fixes an issue (#1808) where the replies button overlaps the license message when the editor is switched into edit mode. 

This is achieved by only applying the negative margin on the `thread-reply` element when the annotation is in "view" mode.

An `on-mode-change` handler is now passed to the annotation directive via an attribute which is called when the view mode changes. A class applying the negative margin is then toggled on the reply element in the thread template.
I think what's going on (but I haven't read that closely, so maybe I'm wrong), is that the callback is being called inside the digest cycle of the annotation (but the thread is not digesting). But digests recur downward, so you while the thread isn't in a digest cycle, trying to digest its scope will also digest the annotation, which is already digesting.

You can get around this by just use `$scope.$evalAsync`.