More filtering options (based on Pose2Sim)

Sports2D now uses the Pose2Sim filtering code. This is better, as when new features might be added, they will only need to be brought in one place (in the same way as the Sports2D scaling and IK code is dependent on Pose2Sim)

• Added optional Hampel filter for outlier rejection, to be run befur further filtering methods.
  Rejects outliers that are outside of a 95% confidence interal from the median in a sliding window of size 7.

• Added GCV spline filter. Automatically determines optimal parameters for each point, which is good when some move faster than others (e.g., fingers vs hips). User can make it biased towards more smoothing (>1) or more fidelity to data (<1) by adjusting the smoothing_factor.
  Might severely under or over-smooth due to numerical precision issues, so use with caution. I could not figure out a way to make it more robust, even after normalizing time and/or the observed y values. Feel free to intervene!
  Acts as a Butterworth filter if cut_off_frequency is set to an integer instead of 'auto'.

• Fixed Kalman filter. Simplified version, the user says how much more they trust triangulation results (measurements), than the assumption of constant acceleration (process)

• The available filters are now: Butterworth, Kalman, GCV-spline, LOESS, Median, Gaussian, Butterworth on speed

Full Changelog: v0.8.16...v0.8.17