Oculus Rift|libappfw|libgui: Frame buffer should not use mipmapping

The main problem with the LibOVR rendering was that the frame buffer
texture had mipmapping enabled; GLTexture never applied the parameters
because the texture wasn't bound using the class.

OVR rendering is now (de)initialized as needed from libappfw.

Todo: Reconsider ownership of the unwarped frame buffer.