[bin/inbox-sync] Add an option to start or stop all accounts.

Summary: This adds the "--all" option to the inbox-sync command as requested by @pavelbinar

Test Plan: review the code, try the "--all" option with and without and email address as well as skipping the "--all" option.

Reviewers: emfree

Reviewed By: emfree

Differential Revision: https://review.inboxapp.com/D333