add low pass filter to meas airspeed driver including logging of filtered value
Merge remote-tracking branch 'upstream/master' into diff_press_filter

Conflicts:
	src/modules/sdlog2/sdlog2.c
fix logging of filtered diff pressure signal
Merge remote-tracking branch 'upstream/master' into diff_press_filter

Conflicts:
	src/drivers/meas_airspeed/meas_airspeed.cpp
Merged airspeed filtering from Thomas Gubler