Copter: rename control_modes.pde to switches.pde
Copter: Thr and Batt failsafe disarm when landed

When throttle/radio failsafe or battery failsafe are triggered, the
vehicle will disarm if it is landed even if the throttle is not at zero.
Auto mode will disarm if landed and mission has not started.  This
ensures that the vehicle does not disarm during a mission land command
that appears mid way through a mission.