Impress LibreOffice OpenGL Slide Transitions under Wayland via GTK3

Impress LibreOffice OpenGL Slide Transitions under Wayland via GTK3 (GtkGlArea).

So I've implemented enough to get this working on my machine now. I've demoed "static", "glitter" and "honeycomb" above from my -O0 debugging build. I'll work on merging this to master now, patches are in our gerrit instance. Porting from glew to epoxy is a necessary step, I know it builds on Windows and Mac, but that's utterly untested.