Refactor: move common command line arguments to base class

[k-dominik]

Summary:

• moved all common command line arguments to base class
• explicitly specify --raw_data flag for Pixel Classifcation
• specify the --readonly flag
• specify the internal export path as exported_data

fixes #50, #49

[k-dominik]

Thank you very much for looking at it @wolny!

I'll test it once with all workflows before merging!