Replace GraphWindow's title bar icon with standard 16x16 app icon

[GoogleCodeExporter]

Strangely, when running in Eclipse JInternalFrames (which GraphWindow extends) 
use 12x12 icons instead of the expected 16x16.  As such, in r138 I created a 
12x12 icon just for use in GraphWindows.  As I have come to find out, however, 
when compiled to a .jar file JInternalFrames instead use 16x16 icons (as would 
be naturally expected).

Therefore we should return GraphWindow to using the standard 16x16 app icon, as 
most of VisiGraph's users use it in its compiled form, and I suspect 16x16 is 
also the default size for icons on Macs.

Original issue reported on code.google.com by 0x24a53...@gmail.com on 8 Jul 2011 at 8:11