[WIP] GTK 3 Looking Glass Alternative

The build-in Javascript Looking Glass is quite limited in functionality, and extending it would require a lot of new ui elements, which would mean a lot of work.
So I thought it'd probably be nice to have it a standalone application instead.
This has the advantage that you can use it to some extend with cinnamon broken.

This version uses Python and GTK 3 to create a guake-like looking glass.
It currently has most of the functionality of the original and some additions the original does not have.
This is a work in progress, I need to do a lot of cleanup before it's ready, but for those who might want to try it out, I thought I'd create a pull request.

Currently it runs alongside the javascript version. 
Screenshots: http://lusito.info/sight-beyond-sight5.png

I did remerge this back into mint-master from #1476, I hope I didn't miss anything or mess anything up, so be careful trying it out.
I checked the github diff and it seems to be ok. Hopefully #1476 will be pulled before I finish this one.