Extend Bella's functionality

* Knows  about undo & redo
* Will also destroy your document formatting too!
* Can cut, copy & paste
* Bella is a tidy cat and likes valid documents
* Bella can be hooked up to use an existing cursor
* Custom actions to be loaded externally
* Has AMD integration
Add workaround for crashing TrivialUndoManager bug

TODO - raise an issue about this!