Use typedefs for smart-pointer types in sensor project.
Use smart pointers to const interfaces where applicable.
Merge branch 'use-typedef-for-smart-pointers'

Conflicts:
	sensor/src/classes/alt_imu.cc
	sensor/src/classes/i2chandlers/acc_and_mag_handler.h
	sensor/src/classes/i2chandlers/gyroscope_handler.h
	sensor/src/interfaces/i2chandler.h