Rework Object handling to better map to reality

[SaladDais]

Right now objects are handled at the region level, which breaks handling of sim->sim object crossings. The proxy also assumes that whatever region the objectupdate was received from is the owner of the object it's updating, which isn't correct. indra only goes off of the RegionHandle in the body of each ObjectUpdate type, and that's what triggers object handoff. Getting an Object's global pos isn't possible either because they don't know what region they belong to.

Need to:

• Store region handle on objects so they know what region they belong to and can calculate their global position
• Switch to doing internal lookups by FullID. LocalID + Handle is only ever used to lookup the FullID in indra. Any update could potentially change an object's localid
• Move ObjectManager to Session. That model works better for region handoff. Keep something simple on the region so lookups by localid can still be done?
• Handle region handoff correctly and add tests

[SaladDais]

Fixed by ebc02f9