Added periodic switching support

Building with autoSwitchSpacing & autoSwitchDuration both > 0 will cause
a switch from RW to VR, of duration autoSwitchDuration, every
autoSwitchSpacing. Manual controls (A, B, right trigger) override the
auto switching & all manual controls reset autoSwitchSpacing so that a
manual switch will never be followed by an auto switch less than
autoSwitchSpacing seconds later.