screenshot upldates

git-svn-id: https://plugins.svn.wordpress.org/images-thumbnail-sliderv1/trunk@820666 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme.txt changes

git-svn-id: https://plugins.svn.wordpress.org/images-thumbnail-sliderv1/trunk@820667 b8457f37-d9ea-0310-8a92-e5e31aec5664