Argparse import

This swaps the bash-style opt parsing for python standard argparse

Forked from work in !84 (merged)

This MR proposes some CLI changes:

• remove conflicting -s -d flags & required checking logic in favor of choice switch --mode [singularity|docker], matches args for benchmark-suite
• implement PEP8 Module dunders for standard way to access module version number, print(hepscore.__version__)
• drop py2 test - further removal of obsolete py2 methods for another MR