Added support for specifying valid argparse choices  with Argument node in pipeline.
A lot of changes to the pipeline to make parameters consistent and each pipeline do less.  Pipelines were split to add flexibility.
ShadeCorrection uses nornir_imageregistration instead of ImageMagick.  Users only specify brigtfield or darkfield shading correction.  No more fiddly options.
Pyramids now auto-generate missing levels if possible.  This makes pipeline invokation simpler since users don't need to ensure the pyramid is built at the correct level first.