alohaWidget: Trigger change event whenever the editable is modified

Aloha needs some special treatment to get notifications about every
content change. The smart content change event is not triggered for
formatting actions and other changes.

This change implements a way to get all modifications as mentioned
in https://github.com/alohaeditor/Aloha-Editor/issues/696
Merge pull request #198 from chlu/fix-alohaWidget

alohaWidget: Trigger change event whenever the editable is modified