fpavogt/brutifus: Improved WCS routine efficiency

v2019.08.2: F.P.A. Vogt

• improved the WCS function, to minimize memory use in crowded fields.
• full restructuration of the high-level operation of the code, with proper entry point, via a new run() function
• split the WCS correction function, so that it can also be used (potentially) as a stand-alone tool for 2D images.
• started using pylint ... ouch!
• worked on the plotting routines, to make them more robust and uniform.