Ported Tao.OpenAL/OpenGL to SDL2

* http://www.mono-project.com/Tao is long gone. This eliminates it completely.
* https://github.com/flibitijibibo/SDL2-CS does have enough OpenTK parts already.
* This also replaces the legacy ARB_ extensions with core OpenGL functions.
* Added some hints from the https://github.com/OpenRA/OpenRA/wiki/FAQ for more helpful logs.