Merge branch '1353-6-dof-headtracking-not-described-in-readme-txt' into 'main'

The yaw angle rotates around the z axis, the pitch angle rotates aroud the new y axis, and the roll angle 

rotates around the new x axis.

In case of 6 DoF support for rendering, the head rotation trajectory file may also include a listener 

position in absolute Cartesian coordinates on the x-, y- and z-axis. Note that the listener position is 

expressed in absolute coordinates, while the listener orientation is expressed as scene displacement. 

An example line from a headtracking file of a listener facing forward, positioned at x=3.0, y=4.0 and z=0, 

could be:

-3.0,0.0,0.0,0.0,3.0,4.0,0.0

Note that the listener position applies for listener orientation expressed both in Quaternions and Euler angles.

For the Head rotation operation modes, external trajectory files are available:

headrot.csv