Convert to using click instead of argparse

[nphilipp]

Story

As a regular contributor to Fedora Infrastructure projects,
I prefer them using the same basic building blocks,
so I don’t have learn five things of the same type.

Acceptance Criteria

• The CLI interface is implemented using click …
• … and allows tab completion using 'click-complete'

Background

This meshes with #67, click lets us put the CLI bits near their logic counterparts instead of having to build a CLI argument parser monolithically in one place. Additionally, using click-completion we can easily get tab completion on the command line.