Add method to calculate angular velocity and save it to the csv

[lauraporta]

Is your feature request related to a problem? Please describe.
It would be useful to know the angular velocity of the mouse head at every frame

Describe the solution you'd like
I made this draft method:

def get_angular_velocity(angles, sampling_rate):
    #  angles are in degrees
    # angles = np.deg2rad(angles)
    diffs = np.diff(angles)
    #  remove outliers
    diffs = np.where(np.abs(diffs) > 0.05, 0, diffs)
    angular_velocity = diffs / sampling_rate

    return angular_velocity, diffs


angles_array = derotate.interpolated_angles
sampling_rate = 1 / 179200  # 1 / Hz

angular_velocity, diffs = get_angular_velocity(angles_array, sampling_rate)