Copter: crash checker

Crash is determined to have happened when the copter is 20deg more than
the ANGLE_MAX parameter continuously for more than 2 seconds
Not activated when in ACRO mode or while flipping
Copter: add alt and throttle checks to crash detector
Copter: remove some commented out send_text code
Copter: correct @Range of MOT_TCRV_MAXPCT parameter