Keeps Stokes throughout postprocessing

[thomaswilliamsastro]

This PR fixes the unnecessary slowdowns that come with re-adding degenerate axes throughout postprocessing.

CASA now typically crashes if the images don't have 4 axes in, which it didn't use to. So we now spend a lot of time ripping them out and putting them back in, which can take a long time for big cubes. Now, we just keep the Stokes axis in throughout, dropping when we export to fits at the end.

This also finally fixes the feather/feather_before_mosaic logic:

• If feather is True and feather_before_mosaic is False, it will feather together individual mosaic tiles, as well as mosaicking the interferometric and singledish data before feathering those together for the final mosaic of mosaics.
• If feather is True and feather_before mosaic is True, then it will instead mosaic together the feathered individual tiles. Note that if feather_before_mosaic is True, it will still create the full singledish image, but will not use this for the final mosaic.

Fixes:

• Fix bug with has_memory_issue call
• Ensure coordinate axes between interferometric/singledish data match up when staging in postprocessing
• Fix pixperbeam in trim cube to actually respect min_pixperbeam
• Remove dropdegaxes calls, since we don't use them any more
• ccr_dropdeg has now been renamed to ccr_importfits, and modified to either import a fits file or just copy over
• Fix logic with feather_before_mosaic

[codecov]

Codecov Report

❌ Patch coverage is 4.25532% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 6.28%. Comparing base (8224025) to head (a397fbc).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
phangsPipeline/casaFeatherRoutines.py	0.00%	13 Missing ⚠️
phangsPipeline/handlerPostprocess.py	7.69%	12 Missing ⚠️
phangsPipeline/casaMosaicRoutines.py	0.00%	11 Missing ⚠️
phangsPipeline/casaCubeRoutines.py	10.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #353      +/-   ##
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+ Coverage    6.27%   6.28%   +0.01%     
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  Files          38      38              
  Lines       15242   15209      -33     
  Branches     3664    3654      -10     
=========================================
  Hits          956     956              
+ Misses      14272   14239      -33     
  Partials       14      14              

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