added undo / redo functionality to demo. Still needs to be tested.
Simplified event firing mechanism
Initialize userId correctly in new events
Fixed bug with CollaboratorLeft event
Fixed targeting bug in fireEvent()
Fixed some bugs and test cases
Fixed redo/undo stack
Make redo/undo event non-local so changes are updated in the GUI
Merge branch 'master' of github.com:mkrause/gx into BaseModelEventRefactoring

Conflicts:
	src/gx/realtime/CollaborativeObject.java
	src/gx/realtime/EventTarget.java
	src/gx/realtime/Model.java
added javadoc to the Model