Concatenation method

[andreped]

There are numerous scenarios where it might be of interest to apply a concatenation, especially of images/segmentations. I found that in the FlowNetwork script there is a PO called ImagesToSequence, which seems to do a concatenation along the "time" axis:

FAST/source/FAST/Algorithms/NeuralNetwork/FlowNetwork.cpp

Line 53 in 5b88fcc

void ImagesToSequence::execute() {

However, there is not an option to set which axis to concatenate along. It should also be easy to concatenate multiple elements simultaneously, similarly as done in numpy:
output = np.concatenate([x1, x2, ...], axis=k)