Add user-based persistance

[mwfarb]

Since users are given session based names it's hard to store persistent data to modify their personal avatars since the object name is always changing and attaching an object to a parent. To resolve:

• Add persistent store by username, not camera name.
• Consider anonymous user model.
• Consider authenticated user model.
• Consider parent/child use case of each object.
• Consider storing values based on one scene, one namespace, or entire arena.