Add a folder system for graph functions

[GoogleCodeExporter]

As the number of standard graph functions runs past 40, the need for additional 
mechanisms for cleanly grouping and sorting them increases.  Also, with the 
addition of algorithm-specific variants (see Issue #118) and (possibly) 
iterative instructional, the number of expected algorithms will soon begin to 
balloon.

As such, some sort of system should be devised to cleanly collect related 
functions into coherent groups (e.g. MST, Routing, Network flow, Coloring).

This should be reflected not only in the downloads dialog, but also the 
function menus and local script file structure.

Original issue reported on code.google.com by 0x24a53...@gmail.com on 1 Jul 2011 at 2:34