Refactor, tidy up html output, add support for thumbnails

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@774579 b8457f37-d9ea-0310-8a92-e5e31aec5664
Tidy up html output

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@774580 b8457f37-d9ea-0310-8a92-e5e31aec5664