RFE: Migrate from PyGTK to GTK3 & PyGObject

[ryran]

_GTK+ v2 and PyGTK? Lame! Should be using GTK+ v3!_

[ryran]

Yes. I wrote Pyrite with PyGTK because it was easy -- path of least resistance.

The next time I can invest some time in Pyrite, I'll absolutely be aiming for this first.

[stokito]

See #31