Rename AppData file to match .desktop file

This is as per spec:

http://people.freedesktop.org/~hughsient/appdata/
Revert "Asynchronously load VM sources"

This patch broke launching of VMs from commandline and therefore
from gnome-shell search results as well. Reverting it for now but lets
re-implement it in a more robust way later.

This reverts commit 14484a31f775d73412cd49dd42e8baae5e75366f.

https://bugzilla.gnome.org/show_bug.cgi?id=706742