Draft: Implement intermediate resolution widefield imaging

This implements the intermediate 1-2" angular resolution imaging as a pipeline step. It is intended to be run after direction-dependent calibration has been done. Its output will be an image of the field. The output can later be reused for the facet subtraction needed for the sub-arcsecond resolution imaging.

First merge !76 as that provides delay-calibrated MSes that serve as the input for this workflow and later imaging steps.