Resolve "Add utility script for comparison of regression test data"

This MR adds a utility script for the visual comparison of old (truth) and new (test) trajectories for our regression tests.

3 kinds of Errors are detected:

1. The person has no counterpart in the other file
2. The person has a different first/last frame than the corresponding person in the other file
3. The person differs from the other in one point with an euclidean distance of at least 1 pixel (currently not user-definable)

For the first case, you see the trajectory of the person who didn't find a match (yellow for truth; pink for test) and trajectories which could have matched, but didn't from test and truth. If you can see that there are a test and a truth trajectory drawn as well, the difference is probably that the person was double tracked in one but not in the other case.

For the second and third you just see the 2 trajectories (green: truth, blue: test).

You see each paring only once, i.e. if 2 people have different start and end frames, you still watch them once.

One goes to the next pairing by pressing n.

NOTE: You need to install opencv for python (used for undistortion)

Closes #216 (closed)