Remove JSON OT clone() function

The clone function in the JSON OT code isn't ok:
- Its slow
- It requires browser support for JSON
- It shouldn't be necessary, damnit

It should be removed.

To do so, we'll probably need a way to properly roll back operation application. If an op gets half-applied, then an exception is raised during processing, we should instead invert the applied op components and apply them to restore the state.