PX4: added support for the MPU6000 on the v2.4 Pixhawk
SITL: Add barometer drift parameter to the SITL library
SITL: Wire in random noise and fixed drift for the SITL barometer
SITL: Wire in basic support for SITL downward-looking sonar sensors
SITL: Add noise and glitching behaviour for the sonar sensor
SITL: moved airspeed pin to pin 1

keep it separate from the sonar, allowing both to be used at the same time
AP_Airspeed: changed default pin for SITL to pin 1

this leaves room for the sonar
Plane: added sonar logging to dataflash
Plane: added MAVLink sonar logging