version 1.5.3 - fixed admin notice and better contact form 7 integration

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@859079 b8457f37-d9ea-0310-8a92-e5e31aec5664
fixed add to form button not working

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@859370 b8457f37-d9ea-0310-8a92-e5e31aec5664