Fix Mac OS X SDL.framework and allow HMD rendering with Oculus VR

There was a problem on Mac OS X with how the binary dynamically loaded the SDL.framework (it didn't work on systems without SDL, even though the SDL.framework was included in the application bundle). I've included the SDL.framework in the git repository, along with the ability to build and link the Oculus SDK from the QuakeSpasm Xcode project.

I've also separated the initialization of the HMD rendering and the Oculus VR to allow for debugging the HMD rendering without a unit.

Sincerely appreciate your work putting this together! I'm looking forward to experiencing it myself once I get my hands on a rift....