Include utils for 3D stereo calibration

[sfmig]

Describe the solution you'd like
It would be nice to include utils for 3D stereo calibration of two or multiple cameras, so that 2D tracks can be expressed in 3D space.

Describe alternatives you've considered
DeepLabCut provides support for 3D stereo calibration with 2 cameras, and anipose/aniposelib provide support for more than two cameras.

Additional context
I was surprised that I didn't find a 'clear' (i.e., popular, actively maintained) library using python and opencv to carry out stereo calibration, as far as I understand it is a fairly common and standard procedure. From my search it seemed that people either turned to Matlab's toolbox or scripted their own solution with python & opencv, but I may have missed something.

I think it would also be very helpful to include recommendations on how to best collect the calibration data (this tutorial is a good reference, and also the intro in this paper)

[niksirbi]

@sfmig should we close this, as it's likely to be a feature of https://github.com/neuroinformatics-unit/ethology? We can copy this issue over there.

[sfmig]

yes sounds good. Is there a fancier way than copy/paste?

[niksirbi]

No idea, if there's a trick @adamltyson probably knows it.