gtk3, wayland, opengl, glew and epoxy

[Caolán McNamara]

locally I have our opengl slideshow transitions working[1] under gtk3
on wayland and I'd like to merge this to master. The gtk3 part is
fairly trivial as it turns out. But glew doesn't work under wayland.
epoxy does however (and it's what gtk3 itself uses). epoxy claims to
support all of our platforms. One little snag is that libgltf uses glew
in its headers, so I had to patch it to port it over to epoxy.

Is there any objection to the principle of dropping glew in favour of
epoxy, or do I need to go down a more complicated conditional approach.
Or any other snags I haven't considered ?

C.

[1] well some of them anyway