Added option to turn of unsubscribes entirely. If you manage multiple lists in MailChimp and have users subscribe outside of WordPress, you may want to choose No so contacts aren't unsubscribed from other lists when they register on your site.

git-svn-id: https://plugins.svn.wordpress.org/pmpro-mailchimp/trunk@788219 b8457f37-d9ea-0310-8a92-e5e31aec5664
Setting defaults on activation

git-svn-id: https://plugins.svn.wordpress.org/pmpro-mailchimp/trunk@788220 b8457f37-d9ea-0310-8a92-e5e31aec5664