Copter: disable some aux channels on hexa and octas

Resolves issue #324
RC_Channel: formatting
Copter: rc10, rc11 available even without MOUNT
Copter: default Ch7 to DO_NOTHING

Ch7/Ch8 Save_WP feature triggers when switch is brought high (instead of
low) to be consistent with other aux features
Copter: more Ch7/Ch8 event logging

Additional event logging for SaveWP, Fence, Acro trainer, Save Trim
Copter: recalc distance to home during arming

fixes an rare edge case in which the fence could trigger immediately
after arming
Copter: disable autotune if pilot moves yaw stick
Copter: arming check that throttle is above failsafe