Enabling OpenGL ES 2 shader support by default

If you need to use OpenGL ES 1, you must recompile the NME native binary using -DNME_FORCE_GLES1. Perhaps, it would be possible to automatically roll back to OpenGL ES 1 by dynamically loading the GL library, but for now the binary is hard-coded to compile against GLES2 (default) or GLES1 using the above flag.