[321/906] add OpenGL ES 2.x support.

[321/906] add OpenGL ES 2.x support.

In OpenGL 2.x for Embedded System, a lot of basic scene/draw functions
have been removed. It means that everything is made using vertex and
fragment shaders.
I have also added a gstglwindow backend for winCE that uses EGL
(Native Platform Graphics Intercace) (which is a full part of
OpenGL ES specification). It remove the use of wgl/glx functions.