pybullet: added EGL render device and window_backend option.

EGL review.
EGL dynamic loading, windowType to int
moved to glad2
Require GL 3.3 as GLInstancingRenderer.cpp uses glVertexAttribDivisor
glad2 update with dynamic X11 added
removed old file
build fix
fix mac/win
EGL w/o c++11, off by default
fix premake
fixup: premake fix 2

test/GwenOpenGLTest/OpenGLSample.cpp

@@ -356,7 +356,7 @@ int main()
 #ifndef _WIN32
     //we need glewExperimental on Linux
 #endif // _WIN32
-	gladLoadGL();
+	gladLoadGLInternalLoader();
 #endif
 #endif //B3_USE_GLFW
     //we ned to call glGetError twice, because of some Ubuntu/Intel/OpenGL issue