Add simple half-acquisition CoR finding algorithms

There exist simple algorithms for finding the CoR of half-tomo acquisitions, which were developed and tested over the beamlines for years. These algorithms are usually quite simple, which means easy to diagnose and fast results.

@nemoz has contributed one of these, and it should be integrated in nabu/preproc/aligment.py

Code and test data can be found at the following paths on the ESRF cluster: