Add ATTITUDE_QUATERNION support

[vooon]

As i understand (from #49) conversion was this: NED (w x y z) -> ROS ENU (x -y -z w).

Related #68.

[TSC21]

How can we give a test to this?

[vooon]

Need enable ATTITUDE_QUATERNION stream, but it require custom rc script.

[TSC21]

So it needs to be activated in PX4 side right? What kind of script are we talking about?

[vooon]

Special copy of /etc/init.d/rc.usb.

[TSC21]

Should check https://github.com/PX4/Firmware/blob/master/ROMFS/px4fmu_common/init.d/rc.usb, add ATTITUDE_QUATERNION stream and make a PR. But you should know that by now for certain 8)

[TSC21]

New message definitions have ATTITUDE_QUATERNION_COV. Do you think adding covariance will get any advantage?

[vooon]

I could be useful. But still no covariance data for gyro, and still acceleration data not included.