Update: WordPress 4.0 compatibility

git-svn-id: https://plugins.svn.wordpress.org/simple-lightbox/trunk@980337 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update: WordPress version requirement to 4.0

git-svn-id: https://plugins.svn.wordpress.org/simple-lightbox/trunk@980409 b8457f37-d9ea-0310-8a92-e5e31aec5664