BUG: `.centroid` does not wrap for angles

[bifbof]

In #431 we discovered an error in calculating the mean angle for a location. We calculate the average coordinates with .centroid. This function assumes that the coordinate system is projected and therefor does not wrap around in a circle. For example, if we compute the centroid of the multipoint [(0, 179), (0, -179)], we get the point (0, 0) instead of the desired (0, 180). This is equivalent to this problem (https://rosettacode.org/wiki/Averages/Mean_angle), for a geographical explanation see (https://carto.com/blog/center-of-points/). A suggested solution would be to implement a new function in util.py. You can also take a look at https://github.com/mie-lab/trackintel/blob/4f4868b6547bfceb05447e221bb681f8cd389fd7/trackintel/preprocessing/positionfixes.py#L455 That suffers from the same bug.