Bugs fixed:
1. The test for removing small trajectories was wrong. It was checking if in either direction size was smaller than a threshold, but it should reject a trajectory if both the dimension have small standard deviation.
1 a. This can lead to reduction in threshold for removing trajectories.
2. The trajectory direction was reversed and not compatible with Wang.

Added:
display_2D_trajectories.m: This is generic code for drawing trajectories for a frame. It can be used by both mocap trajectories and Wang trajectories.