Add pre-processing steps to PedPy

[schroedtert]

When using PedPy for analyzing trajectory data from experiments, some pre-processing steps might be useful to compute better results:

• smoothing of trajectories, e.g., remove jitter from the trajectories
• pull trajectories inside the walkable area, e.g., when using head trajectories the person may lean over boundaries. In such cases the trajectory should be pulled back into the given walkable area. There was a script for this purpose, we should reactivate it.