Make Q and U frequency cubes from WSClean outputs

[vijaymahatma]

Concatenate/stack the Q and U channel images produced by WSClean into two frequency cubes containing Stokes Q and Stokes U. Also produce a frequency.dat file with a list of frequencies contained in these cubes (later needed for rmtools).

The outputs of this are inputs to RMSynthesis using rmtools.

[emaderubeis]

We produced a Python script to concatenate the channels images in Stokes Q and U from WSClean. WIth this, we also produce a list file with channels frequencies and with the average Q and U rms noise per each channel, to be provided to RMtools. Blank channels are removed in the cubes and lists.
Script for Stokes Q and U cubes concatenation, with noise evaluation: https://github.com/LOFAR-VLBI/pilot/blob/add_qu_imaging/scripts/make_pol_cubes.py

[emaderubeis]

The make_pol_cubes.py has been harmonized with CWL requirements of the relative CWL step (concat_pol.cwl) and the main CWL workflow. Moreover, the script checks also the rms noise level of each channel (average between Stokes Q and U) with respect to the median value and automatically excludes channels above 5*median(rms).

Ongoing tests on personal dataset.