Meet Bella. She will destroy your documents.

* Supports multiple instances in the same doc
* Able to exercise entire selection controller
* Can say meow (and other text manipulation actions)
Using a real SessionController causes problems with double-events
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!
Add checks to ensure the cursor is in a valid step

Issue highlighted in review of PR #451.
Add a seeded random number generator to allow reproduction of crashes

Original source: https://github.com/davidbau/seedrandom