Copter: fix to dcm-check to be continuous

dcm-check was triggering after 10 bad headings but these did not need to
be continuous meaning if the vehicle was flown long enough it would
almost certainly trigger a dcm-check failure and land
LogAnalyzer: balance/twist initial commit
LogAnalyzer: updated testCompass to match our prearm check
LogAnalyser: TestBalanceTwist sanity check of motor values
LogAnalyser: rename BalanceTwist to MotorBalance
AC_AttControl: add sqrt_controller

Original code by Jonathan Challinger
AC_AttitudeControl: use sqrt_controller function
AC_PosControl: Use sqrt_controller function
AC_AttitudeControl: cleanup angle_ef_roll_pitch_rate_ef_yaw_smooth
AC_PosControl: use AttControl's sqrt_controller
AP_NavEKF: fix parameter descriptions

Errors pointed out by Richard (DK)
Copter: ReleaseNotes for AC3.2-rc14
LogAnalyzer: Binary Logs may end with \xff
 - ignoreBadlines can be used to assume this is a proper EOF
LogAnalyzer: write \xff EOF assumption to stderr
LogAnalyzer - Improve Autotune Test
 - previously version could report failed autotune sessions as valid and
   valid sessions as failed
Copter: don't stop logging on disarm when LOG_WHEN_DISARMED is set
AHRS: add reset_gyro_drift method
Copter: reset ahrs gyro drift after gyro calibration
AP_GPS: Add agcCnt to UBX1 message
Frame_params: 3DR_X8+_RTF.param

Adding param file for 3DR X8+