Do not display the initial and terminal nodes in the GWT model

[GoogleCodeExporter]

By default the GWT model should not show the initial/terminal nodes and should 
denote the initial/terminal partitions in some other way (e.g., double circles 
for the terminal partition).

There should probably be an option to show the initial/terminal nodes (may be 
useful for tracking the starts/ends of the model).

Original issue reported on code.google.com by bestchai on 25 Jan 2015 at 11:45