session controller: on sign in redirect user to homepage unless they have a user account in db or a coop has been set previously in the session to allow for the user to be added to the coop. if new user, set the coop to the coop set in the session.
User-Coop: use a rails association for user coop relationship instead of a manual assignment
coop: coop has member_join_hash and admin_join_hash for generating urls for users to join the coop
user: email is sent to alert user of new account just after account creation
homepage: if signed in redirect to user's coop. if not show a list of coops to pick from (so that their calendars may be viewed)
user form: user can no longer edit their coop, user can add a phone number