GtkWindow: clean up button event handling
GtkWindow: clean up button event handling

We were not translating event coordinates to the toplevel
window, thus the regions we determined were not right.
We were also not respecting the maximized state, and we
were unnecessarily refusing to handle events when not decorated.
https://bugzilla.gnome.org/show_bug.cgi?id=696197

Lyude/gtk-,jessevdk/gtk,ebassi/gtk,Sidnioulz/SandboxGtk,bratsche/gtk-,ahodesuka/gtk,davidgumberg/gtk,grubersjoe/adwaita,ahodesuka/gtk,Adamovskiy/gtk,Adamovskiy/gtk,Lyude/gtk-,Distrotech/gtk2,jadahl/gtk,msteinert/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jigpu/gtk,bratsche/gtk-,chergert/gtk,Distrotech/gtk2,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,bratsche/gtk-,davidgumberg/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,chergert/gtk,grubersjoe/adwaita,bratsche/gtk-,Distrotech/gtk2,Sidnioulz/SandboxGtk,grubersjoe/adwaita,ebassi/gtk,Adamovskiy/gtk,chergert/gtk,ahodesuka/gtk,jadahl/gtk,Lyude/gtk-,msteinert/gtk,jessevdk/gtk,chergert/gtk,Adamovskiy/gtk,jadahl/gtk,jadahl/gtk,jigpu/gtk,grubersjoe/adwaita,davidgumberg/gtk,msteinert/gtk,ahodesuka/gtk,alexlarsson/gtk,ahodesuka/gtk,Distrotech/gtk2,jessevdk/gtk,davidgumberg/gtk,ahodesuka/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,ahodesuka/gtk,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,Lyude/gtk-,davidgumberg/gtk,jadahl/gtk,davidgumberg/gtk,ebassi/gtk,Distrotech/gtk2,grubersjoe/adwaita,ebassi/gtk,Distrotech/gtk2,bratsche/gtk-,jessevdk/gtk,msteinert/gtk,chergert/gtk,msteinert/gtk,ebassi/gtk,jadahl/gtk,alexlarsson/gtk,jessevdk/gtk,msteinert/gtk,jigpu/gtk,bratsche/gtk-,grubersjoe/adwaita,ebassi/gtk,Lyude/gtk-,davidgumberg/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,alexlarsson/gtk,jessevdk/gtk,Adamovskiy/gtk,jigpu/gtk,davidgumberg/gtk,jigpu/gtk