Fix header mash up

Some notes:
I could be seriously fucking up some things here, so I apologize in
advance for whoever has to clean up after me. That includes you, future
me.

Anyway, I got rid of most of the serious offenders. I still need
@fuyukaidesu to clean up everything past GtkGraph.hpp (Gomen for making
you do it. I know you were meant to do it starting form GtkSettings*
onwards.)

The code compiles cleanly, but I'm going to look through this one more
time. I'll reference this in the next commit.