I think this is the least intrusive fix for the chat crashes: lock the agent
list when we're updating from the network, simulating, or rendering.  I think
there are likely to be other synchronization issues, but this is a start.
Merge branch 'master' of https://github.com/worklist/hifi
Merge pull request #164 from ey6es/master

To fix chat crash, lock agent list when updating from network, simulating, or rendering.