Add gui draft (not connected to data yet)
Improve joinRoom message to player
Server: don't keep layers object in memory. Read it always from disk.

There was probably a bug: the layers object in memory was never updated,
only created once.
Iterate obj using getOwnPropertyNames instead of for .. in
Fix bug: seting part of the vars in the client overwrites all vars in the layer
Server notifies others when user leaves. Fix joinRoom notifications.