Compilation troubles with OpenGL and newer fedora systems

The newer fedora systems seem (and probably soon all other linux systems) to have a stricter separation between the generic OpenGL interface and the part related to the X window system. FindThirdPartyOpenGL seems overly complex by the current cmake standards, is not in sync between the two instances (minor) and critically include libOpenGL and libGLU but not libGLX which is now required. Otherwise symbols like `glXSwapBuffers' remain undefined during the compilation of e.g. GtkGL.cpp.