* [imu] convert imu subsystems to modules
Also
- get rid of explicit imu init|event|periodic calls in main
- each imu implementation has their own imu_x_init/event/periodic
* [imu] fix some imu modules
* [imu] fix bad paths
* [imu] add imu_common module that every implementation autoloads
and put body_to_imu settings in imu_common module
* [imu] fix imu_ardrone2
* [conf] add imu_common settings module in conf_example and conf_tests
Felix Ruess