Skud/Email newsletter autoresponders

Just figuring out some stuff re: the newsletter, and thought I may as well keep the draft here.

Autoresponders automatically send email to people when they sign up for the Growstuff newsletter. We can set up a string of emails for people to get after they sign up. We can also segment by eg. people who subscribe via growstuff.org (as a member of the site) and people who come to the newsletter some other way.

For now, the most important segment are site members.

Site member autoresponders

 * 1 day after: Thanks for signing up for the newsletter
 * Get the most out of Growstuff
 * How to track what you're planting
 * How to share seeds
 * Posts/Forums
 * NOTE: don't assume they don't know this stuff, they might be older members only recently subscribed
 * Did you know?
 * Your data helps everyone
 * Growstuff is open source
 * How to get involved