This switches party and member ids to also be 64bit ints. This uses
considerably less data and cpu due to being able to use binary websocket
frames, and the server can avoid json deserialization completely.
Also hold member ids instead of party member references in the party
plugin, since the members can be reset if connection is lost, causing it
hold refs to old party members.
Encode location update points into a single int, since the updates are
so frequent.
