We want that the actual command ends its work, and then exits with a proper code

This is to accumulate all possible errors at once

• Fixes #29 (closed) Exit with status code 1, if an error occurs
• Fixes #28 (closed) spdxdebian: Some packages result in a PoolError exception
• Fixes #30 (closed) adding tinfoilhat json
• Move execute methods into its own methods/classes #2 (closed) (partially fixed)