AP_HAL: added support for commandline arguments

useful for log replay, specifying log file
AP_InertialSensor: allow HIL sensors to support multiple instances

this allows log replay to test both sets of sensors on a Pixhawk log
AP_NavEKF: allow log filename to be specified in replay
AP_NavEKF: support dual sensors in log replay, and fix flight altitude
Rover: fix for HIL API change
Copter: fix for HIL API change
Plane: fix for HIL API change
Plane: fixed logging of relative altitude
HAL_SITL: fixed build with new HIL INS API
AP_InertialSensor: enable get_accel_count() and get_gyro_count() APIs for HIL
AP_AHRS : change initialisation requirements for EKF and use dynamic method
AP_NavEKF : Improved stability of Z accel bias
AP_NavEKF : Bug fix for height drift due to timer wrap-around
AP_NavEKF : Changed default IMU bias process noise to use smallest value
AP_NavEKF : fixed bug in height limit range
AP_NavEKF : fixed bug in velocity rate of change filter

This bug meant the velocity rate of change used to scale the GPS measurement variances was noisy and too small