Plane: update to new license boilerplate for GPLv3

we had LGPLv2 in some places, despite the fw being GPLv3
AP_Airspeed: added EAS2TAS in airspeed driver

this keeps the true airspeed ratio in the airspeed driver, which seems
the most logical place
AP_AHRS: added true airspeed support in AHRS

use true airspeed for wind calculations, and allow other drivers to
ask for the current ratio
AP_TECS: use ahrs EAS2TAS for true airspeed
Plane: updates for new EAS2TAS scaling
AP_Airspeed: added example sketch for airspeed calibration
Plane: remove old AIR_START code

this was never used or tested