mint-arena: Load UI data before starting intro videos

This way loading happens while the inital loading screen is shown instead
of causing the last video frame to hang while loading the data.
mint-arena: Don't grab mouse during demo playback
mint-arena: Clean up setting mouse state
mint-arena: Set mouse state in CG_INIT

Otherwise the system curors blinks when cinematic starts.
Also, fix the call to CG_MaxSplitView() in CG_ClearState().