Summary:
Ref T6881. This adds the worker, and a script to make it easier to test. It doesn't actually invoice anything.
I'm intentionally allowing the script to double-bill since it makes testing way easier (by letting you bill the same period over and over again), and provides a tool for recovery if billing screws up.
(This diff isn't very interesting, just trying to avoid a 5K-line diff at the end.)
Test Plan: Used `bin/phortune invoice ...` to get the worker to print out some date ranges which it would theoretically invoice.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T6881
Differential Revision: https://secure.phabricator.com/D11577
