Admin-roles with multiuser switch

### Adds:

* deployment instructions for heroku
* some updated gems (ostatus, ratom)
* admin page (admin is the first account created)
* toggling of new accounts by admin
* updates twitter gem and fixes twitter push

People should now be able to deploy their own nodes easily and for no cost through Heroku and it should be adequate for single-account cases. MongoHQ is 512 MB for free, which is more than enough for single-account rstatus purposes.

### Acceptance Tests added:

* should create the first user account as an admin
* redirects first user to admin page after signup
* admin page is accessible by admin users
* admin page is not accessible by non-admin users
* admin page allows you to turn on multiuser setting
* admin page allows you to turn off multiuser setting
* admin page allows you to see the current multiuser setting
* must not allow user creation when there are Users and multiuser is false 

### Admin model tests added:

* Admin#can_create_users? must not allow user creation when there are Users and multiuser is false
* Admin#can_create_users? must allow user creation when there are Users and multiuser is true
* Admin#can_create_users? must allow user creation when there aren't Users and multiuser is false
* Admin#can_create_users? must allow user creation when there aren't Users and multiuser is true

### User model tests added:

* User#admin must not be true as default
* User#admin? must return true when admin is true
* User#admin? must return false when admin is false

### Currently deployed at:

http://status.wilkie.io
maybe call this `redirect_if_not_admin` or something like that?

Or two methods:

    def logged_in_as_admin?
      logged_in? && current_user.admin?
    end

    def redirect_unless_admin
      unless logged_in_as_admin?
        redirect_with_sorry(opts)
        return true
      end
      false
    end