Only show crop tab on WP3.9+

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@959972 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix styling in old WP versions

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@959973 b8457f37-d9ea-0310-8a92-e5e31aec5664