renamed heading controller to wheel controller, added groundspeed dependency and separate parameters

- added parameter to specify which heading to keep on runway
- validate terrain alt before using it

SITL: fixed control callback

VTOL: bench testing without airspeed reading

Improved sensor failsafe reporting 

Commander : Effectively track failure reporting and handle hotplug sensors

UAVCAN footprint reduction

Since mtd already checks whether CONFIG_MTD_RAMTRON is set in
defconfig use this define to check whether to call ramtron_attach()
or at24xxx_attach() in the main function, instead of checking
CONFIG_ARCH_BOARD_PX4FMU-V1.

Also instead of using #ifdef CONFIG_ARCH_BOARD_AEROCORE to determine
whether to start mtd on spi 2 or 4, rather use a new board define
PX4_SPI_BUS_RAMTRON in the board_config.h file.