EKF Cleanup

This is just some cleanup on the EKF. Rename the attitude module from revolution/attitude
since there is nothing revolution specific about it. Changed some constant definitions to be
more consistent.

Also I removed the drift offset fusion between the baro and the vertical gps and simply defer
to the GPS for vertical. This seems more stable for now and we need a different noise process
model for the GPS vertical position if we want to keep trying to fuse between them.