[#55] Shrink the size of the delta updates

* Use 4 byte random generated keys instead of UUIDs (4 bytes vs 37)
* Messages no longer send UUIDs twice
* Remove unneeded 'state' method. Each entity is assumed to be the 'state' of the object.
* Don't update positions of non-moving stuff (Platforms and Powerups were getting sent each time unnecessarily)
* If nothing has been updated, don't send delta updates to clients.