Entity Id Allocation

[DuncanUszkay1]

We need to be able to dynamically allocate regions of the ID space to use for anchor player IDs and communicate these regions when peers connect to each other. The ID space is very large (2bil+) and the number of possible entities relevant to a single player is quite small, so this doesn't need to be particularly efficient it just needs to ensure uniqueness to multiple servers.

There's more to write on this issue, but I'm just getting this down now so I don't forget about it.