Respect OpenGL registry sections. CMake for QMake

I've switched the project's build system from QMake to CMake.
When starting to do packaging and distribution in binary form
CMake can help building installer packages.

Another cool thing is that now more extensions can be displayed.
Where previously a "Error - 404 Not found" appeared for certain
extensions, you'll now see the regular extension specification text.
This is possible now because glxtension respects that different
specifications are stored in different sections of the registry
(See http://www.khronos.org/registry/). Now you can lookup extensions
from OpenGL, OpenGL ES, and OpenGL SC.