Implement feature "frame sharing" for world objects

[benptc]

Implement the body of setFrameSharingEnabled in server.js, and associated user interface changes.

The idea is that you can have a server with a world object that is hosting shared frames.. frames that you place from the pocket onto other objects in the network would be hosted and processed by this world object (hence, this server), iff those objects exist on other servers that don't have a copy of that type of frame. The frames would still be positioned relative to the object they are placed on, but the loading and computation would occur as if it belongs to this server.

As a result, you would only have to update the realityframes of one server to update the frames placed on all objects that it is sharing with.