Safe sensors rate

Prevent arming with unsafe stabilization rates. Whenever stabilization rates change it is compared 
against the gyro rates and updates the sanity check alarms. In addition an infrastructure is added to
pios_sensors for caching the maximum rate so the sanity check doesn't have to worry about the
details of which sensor is on a board.

This provides one part of #1011 but the GCS restriction remains to be done.