Add thumbnail margin

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@881663 b8457f37-d9ea-0310-8a92-e5e31aec5664
Only apply carousel margin to slides

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@881667 b8457f37-d9ea-0310-8a92-e5e31aec5664