Setting and/or console command to enable mirroring

[JeroMiya]

Currently when using direct mode or the render manager even without direct mode, the code plugin does not draw to the window that Unreal creates. When running in the editor (including VR preview mode), we do draw to this window.

Add a console setting or command to the plugin to enable mirroring in standalone mode. This will, for now, draw the undistorted stereo image to the window, while simultaneously drawing to the HMD display (in direct mode or otherwise).