AP_L1_Control: added lateral acceleration interface

this will be used by the Rover code for steering
AP_L1_Control: use a better ground speed estimate at low speeds

this should prevent a rover going in the wrong direction at the start
of a mission
AP_L1_Control: use projected position for turns
AP_Math: update location code to avoid float rounding

this avoids manipulating global coordinates as float variables. Using
a float reduces our precision from 1cm to about 70cm.

This also adds location_diff() which will be used in the L1 controller
to avoid global positions in floats
AP_L1_Control: avoid using float global coordinates

this increases the navigation precision of rovers using L1 control
down to the centimeter level
AP_AHRS: added get_position_lag() call

provide position lag to libraries
AP_L1_Control: adjust position for GPS lag

this should help for rovers
AP_L1_Control: removed _maxf() and _geo2planar() functions

not needed any more
AP_L1_Control: use get_position()
PX4: Adaptations to latest build changes
PX4: Added config file fmuv2 board, not used yet
HAL_PX4: enable right FMUv2 drivers

ets_airspeed is ok, but mkblctrl driver doesn't build yet
PX4: added px4-v2 targets
PX4: added io-v2 targets
PX4: moved px4io-*.bin to ROMFS

this is more convenient than users having to copy it over
PX4: adapt rc.APM for FMUv1 and FMUv2
HAL_PX4: some GPIO functions are not available on FMUv2 yet
PX4: disable bma180 driver for FMUv1
HAL_PX4: fixed build on FMUv1
PX4: enable airspeed base driver and meas driver

this uses the new airspeed parent driver from Lorenz