Split screen editing step 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?
* [ ] Randomise cursor colours to make it easier to see which user is which
* [ ] Let Bella loose in these!

# Pics
![screenshot from 2014-06-17 18 12 07](https://cloud.githubusercontent.com/assets/1052079/3297694/2b1369a8-f5f7-11e3-8be1-98c4d09247f5.png)

Unless the basic approach changed without me noticing, priority is not calculated, but defined, no? And the priority taken for that one spec set over the other can be forwarded all way from `OperationTransformMatrix.transformOpspecVsOpspec` to this method. So not sure where this is misleading? Also do the current callers of this method rely on which set has priority over the other.