Port bin/inbox-* to click.

Summary:
We're already using this library elsewhere, and it's a lot cleaner to
use than argparse. I did some consistency tidying as well.

This is a precursor to modifying bin/inbox-start for multicore support.

Test Plan: ./runtests, manual verification that scripts start as expected

Reviewers: emfree

Reviewed By: emfree

Differential Revision: https://review.inboxapp.com/D254