work in progress:
implemented calculation of covariance Matrix for XY-Cooridantes
of the robot. This is needed, to properly draw the ellipse around
the estimated robot position.
There is now a new function, that will return an object, that contains
position, angle, variance of the angle and three values to draw the
ellipse: large and small radius plus angle of the ellipse.

I could not test it!
And the logfile structure has to be changed for it.