Add packages for Pitivi

Hi.

I was working on packaging Pitivi for MSYS2.
The packages are not 100% ready yet. I wanted you to review them and give me an opinion.
Pitivi needs quite a few patches to open a window, thats why I have used my github remote in the package.
The main problem is that "import cairo" does not work.
I hope I will have more luck with python3-cairo-git, but I have currently trouble building it because setup.py does not have a usefull pkg-config envoirement when calling subprocess.Popen.

I would like to propose some of the patches upstream. But the gobject-introspection hack we have to make in every package (CC=gcc) won*t be accepted upstream I guess. We need to figure out something nice.

Also gtk icons do not work and pitivi still throws many exceptions for simple things.

Would you be interested in merging everything? Or should I put pitivi on a seperate branch?
I can rework the patches and rebase, looking forward for comments.