Update changelog

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@885106 b8457f37-d9ea-0310-8a92-e5e31aec5664
Remove preview.php, use admin-post instead.

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@885107 b8457f37-d9ea-0310-8a92-e5e31aec5664