Split screen editing demo

Usage instructions:

1. Check out this PR or branch
2. Start the server as per normal: ``node webodf/httpserver.js``
3. Point a browser towards http://127.0.0.1:8124/webodf/programs/editor/src-splitscreen.html
4. Log in on both clients (no user validation is performed)

# TODO
* [x] Add support for OT
* [x] Pause/play support to interrupt flow between clients
* [x] Quicker login
* [x] Randomise cursor colours to make it easier to see which user is which
* [x] ~~Fix op priorities so it's per memberid~~ (not an existing problem. My understanding here was flawed)
* [x] ~~Let Bella loose in these!~~ (won't happen in this PR)

# Pics
![screenshot from 2014-06-17 18 12 07](https://cloud.githubusercontent.com/assets/1052079/3297694/2b1369a8-f5f7-11e3-8be1-98c4d09247f5.png)

Calling the callbacks in any case seems wrong to me, it should be only done on final success (or error, but for that we should add an err parameter to the expected callback signature). So far at least all those callback assume success of the inital request.