Rework Widget javascript code to not use a global variable for entry point

[frankduncan]

Currently having two nlogo models compiled to the same page would break as things would get added improperly.

This will involve reworking how the widgets get compiled into javascript themselves, perhaps by some user defined connection between the compiled js and the code widget.coffee. Another option is having the entire session booted up from the compiled netlogo file (perhaps via workspace?) The goForever code that constantly monitors the widgets would either need to take care of all models loaded on page, or a separate goForever timeout would need to be created for each one.