vlada/xfce

Major Xfce refactoring, also adding versions 4.10.*

Signed-off-by: Vladimír Čunát <vcunat@gmail.com>
Merge branch 'vlada/xfce-notg' of git://github.com/vcunat/nixpkgs

This branch refactors xfce and updates it to 4.10. I had been hoping to
find someone besides Vlada to test this (I don't use xfce), but no one
has come forward yet in 2 weeks so if this breaks something they can
make an issue or fix it. It all looks good by inspection.