Implement VBO rendering method

* Kill the Display Lists with fire and replace them with Vertex Buffer Objects
* Divide scenes for static / dynamic rendering
* Bump required OpenGL version to 1.5 (VBO)
* Try to avoid memory leaks in various places

VBO -> CPU, GPU and VRAM usage dramatically reduced ;)

Signed-off-by: Piotr Bocheński <bochenski.piotr@gmail.com>