the parameters were badly out of whack!

used to control board specific parameters, such as PWM output count

In-flight Barometer sanity checking will be a more complete solution but
until then this should catch some bad pre-flight barometer behaviour

Shortened gyro calibration commit also halved the total time we would
look for a good gyro calibration.  This restores the total time to 10
seconds.

when the airspeed ratio is far too low we were not raising it as the
airspeed was never getting above the minimum airspeed

Pair-Programmed-With: Jon Challinger

Trim save gives no feedback, so I've added a gcs_send_text() call to
print "Trim saved" so the user knows to re-center trims again

Removed delays before calibration, reduced number of samples taken,
widened convergence criteria

full rwtest on FMUv2, read test on FMUv1

using update_calibration() instead of the full calibrate() cuts
1.5seconds of the arming time

used to set PWM on motors when disarmed