support for OpenGL 2.0

* use OpenGL 2.0 auxiliary buffers when FBO is not supported, thus this means that OpenGL 3 is not a requirement anymore, so otclient might work in older video cards
* map zooming will never work well with Opengl 2.0 because of glCopyTexSubImage2D limitation

src/framework/graphics/graphics.h

@@ -32,7 +32,7 @@ public:
     void init();
     void terminate();
 
-    bool isExtensionSupported(const char *extension);
+    bool hasFBO();
 
     void resize(const Size& size);
     void beginRender();