level Qt up to version 5.7.0 + several bug fixes

level Qt up to version 5.7.0 + several bug fixes

Qt5-GUI now gets compiled with support for OpenGL,
however only links against GL stubs provided by the
2d software renderer.
That way we can decide at runtime, whether we want to
use GL or not - with almost no overhead, if not.
This also enables QtQuick2 being built correctly,
which depends on GL support and provides the
possibility of using QtQuick2 with the 2d-sw-renderer
even on hardware without native support for GL.