Clean-up model change events

[pjasiun]

After introducing differ we need to clean-up events model and document fire.

1. Current change and changesDone events should be removed.
2. API to add postfixers should be added (see prototype here) and all change listeners which are post fixers should be changed to post-fixers.
3. New document.change event should be introduced, which should be fired after all changes related to the single batch are done. Changes which are executed on the separate batch (i.e. autoformatter) should listen on this event and do enqueueChange().
4. Listeners which really need to listen on each operation apply (live positions, differ) should now listen on applyOperation.
5. We should consider removing data object which is returned by the operation execute, or change it. It made sense when the change event was fired base on the operation applied, but now it might not be needed anymore.
6. model.change event should be private (model._change), is should be used only by the document to fire document.change.