Moved to github

[Alexander Larsson]

In the context of the rename, etc we discussed the hosting situation a
bit and decided to move to github. The mailing list will still be at
freedesktop.org, but the canonical git repositories are now at:
https://github.com/flatpak/

I will also move all outstanding bug reports and pull requests from my
github page and freedesktop.org to the flatpak github organization.

We also have the new webpage on github:
http://flatpak.github.io/

And I have secured flatpak.org which we will point at this.