Split directions

This merge request implements the split-directions segment of the pipeline in CWL, as was worked on in the LOFAR VLBI week in Paris 2023, and is characterised primarily by the split-directions.cwl workflow.

The workflow takes a MeasurementSet (or a list of MeasurementSets), delay calibrator solutions and a catalogue of target directions as its primary input. It performs the appropriate averaging before applying the solutions and then phase-shifting to each of the target directions. Then it refactors that output so that it is sorted by each direction rather than by frequency before concatenating the MeasurementSets for each of the directions. At this point, one can optionally request that the workflow performs self-calibration on concatenated data using the facetselfcal.py script with the auto setting.

The workflow currently outputs the phase-shifted subbands, concatenated direction measurement sets as well as images from the optional selfcal step, both png and fits.