Integrate ANGLE with OpenGL ES 3 support

ANGLE is merging the ES 3.0 development branch to master, as announced here:
https://code.google.com/p/angleproject/wiki/Update20140325

With a working ANGLE OpenGL ES 3 implementation, one would be finally saved from all the trouble one as to go in Windows to access recent OpenGL features not supplied in ANGLE's OpenGL ES 2 - having to mess with GLEW, resizing flicker problems, inconsistent OpenGL GPU drivers, etc.

Since Open ES 3 is fully compatible with desktop OpenGL 4.3, this would provide a solid unification between desktop and mobile OpenGL across platforms.