Add newsletter subscription checkbox
Added wants_newsletter scope to Member

also cleaned up member tests which were using FG.build instead of
.create
Made admin/newsletter page with list of subscribers
newsletter subscription/unsubscription via Mailchimp API
Add text to show we're lovely people and not spammers
split the difference: pre-checked newsletter signup + friendly text
Send Growstuff login_name to Mailchimp

This lets us do mail merges with the member's name, as well as letting
us segment mailouts by people who've signed up for Growstuff and those
who came to the newsletter directly without having a Growstuff account.
Merge branch 'newsletter' of https://github.com/Skud/growstuff into Skud-newsletter

Conflicts:
	db/schema.rb
	spec/models/member_spec.rb