module/x11: remove X11R7.6

to build X11rdp xserver 1.12.99.904 or higher is required therefore
build against X11R7.6 doesn't work anymore.
module/x11: restructured and adapted build

* moved files directly to X11/service from rdp
* required xorg files must now be available in module/X11/service/xorg-server
* added X11/service/xorg-build to help building xorg (see README for details)
Merge pull request #3 from bmiklautz/xorg_build

Xorg build