Change newsletter settings

Change postalAddress, design ({ accentColor, font: sans, serif, or mono, align: left or center }), cleanup, or testRecipients (up to 5). Keys are camelCase. List cleanup is on by default: a subscriber who received afterSends broadcasts in a row without opening or clicking, and has not engaged for quietDays, gets one email asking whether to stay subscribed (subject, body, sent from from or the last broadcast's sender, paid plans only). A week later, anyone who did not click to stay becomes dormant: still on the list, but left out of broadcasts until they open or click again.