Abstraction of green_shoes api from gtk

[zzak]

This is essentially a piece of the white shoes puzzle. An abstracted shoes api which we can spec all shoes implementations against. Since green_shoes is growing rather rapidly, and likely has the most implemented of all the colorful shoes; it's probably the best place to start the shoes api spec.

Also, as green_shoes grows it will need to under go higher level abstraction of classes in order to maintain a consistent and more intuitive object structure.