Make more out of the IMU

[stkdiretto]

As of now, the IMU is only used as a wakeup source when the bike is moved. There is no additional logic for additional states that can be used, e.g.:

• determine whether the bike is actually moving or whether it was just shaken a bit, e.g. because someone else locked their bike next to this one
• determine whether the bike is moving, e.g. in order to keep the GPS powered up and the ESP in light sleep, send location updates every x seconds, and then wait for the GPS to settle at the end of the ride and send one final update