Router UUIDs now properly persisted and synced client/server

This fix effectively does two things:
1. Adds router UUIDs synchronization between client and server. This allows client to perform direct requests to server (at ex. for some GUI activities) using router UUIDs instead coordnates. getMultiPart(world, coord, 6) seems like magic number to me, not counting the fact that block lookup would be slower.
2. Per my prev. investigations, router UUIDs weren't properly stored, or re-generated at each world startup. This should effectively make them persistent.