New feature to hide message for logged in users

git-svn-id: https://plugins.svn.wordpress.org/sitewide-message/trunk@974792 b8457f37-d9ea-0310-8a92-e5e31aec5664
Push Version 0.6

git-svn-id: https://plugins.svn.wordpress.org/sitewide-message/trunk@974794 b8457f37-d9ea-0310-8a92-e5e31aec5664