Copter: renamed MOT_UNSAFE_THR to MOT_SPIN_ARMED

Removed special purpose spin_unsafe function
renamed _throttle_unsafe to _spin_when_armed and changed to an AP_Int8
Copter: implement safety spin for Tricopters
Copter: fix to SPIN_ARMED parameter desciption
Copter: ensure _spin_when_armed is not higher than _min_throttle
Copter: ensure take-off alt is at least 1m

fixes issue #377
AutoTest: rename and remove copter mission files
Copter: initialise ch7 and ch8 aux switches

This ensures that if you have simple mode or sonar attached to an
auxiliary switch it will be enabled or disabled according to the switch
immediately after start-up
APM_Control: allow for a wider range of P values for roll/pitch

values above 1.0 are sometimes needed
AP_SpdHgtControl: rename flybywire_airspeed to airspeed

this variable applies to any automatic throttle mode, not just FBW
modes.

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
AP_TECS: adapt for new airspeed variable names
APM_Control: pass in aircraft parameters and expose coordinate rate offset

this will make it possible to do rate based pitch control without
having a coordinated turn, for in ACRO mode

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
VARTest: adapt for new airspeed parameter names
Plane: pass aircraft parameters to attitude controllers

also cope with rename of airspeed min/max variables

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
Copter: fixed FENCE and WPNAV parameter doc generation
HAL_AVR: fixed example build
VARTest: fixed example build
Copter: Remove CH7 & CH8 Enable / Disable of GeoFence
Tools: add additional divide timing
TradHeli: Rate PID Improvement. Limit Integrator wind-up when PID output is saturated. Also a little bit of general clean-up for readability.
TradHeli: Change to throttle controller to allow swash plate collective to move, even if disarmed, if we are in Acro or Stab.  This is slightly dangerous... as a user could cause a problem if they do not follow the proper usage procedures.  If they do not route the ESC through the APM, but instead direct to Rx.  And then if they do not Arm, they could take off in Stab mode while disarmed, but then when they switch to Alt_Hold, it will drop the collective to the bottom and they will fall.  This can be saved by switching back to Stab.  And it requires operation outside of the normal operating procedure.

This change is being made because most heli users expect to be able to check the swash plate operation before arming and taking off.