Upgrade CM-Example to 3.12

Fixes #191.
This updates the CM used in [`/examples/cm/index.html`](https://github.com/josephg/ShareJS/blob/master/examples/cm/index.html) to to the most current version (3.12), it also fixes one bug and has some small UX stuff in it. See commit list.

The example works still fine for me, loading docs works, changes are persistant and transmitted in realtime,.. tested in FF+Chrome+Opera on OS X.