Port request: Mx

[cooljeanius (Eric Gallager)]

Link: ​https://github.com/clutter-project/mx

It's a clutter-based toolkit. We already have a port for clutter so it shouldn't be too hard to port. Also this is a dependency of ​finalterm which I'd also like to see ported eventually (I'll open a separate ticket for that). I might give it a try myself if I get a chance, just putting this out there in case anyone else wants to write the portfile first...