change names for screenshots & and change readme

git-svn-id: https://plugins.svn.wordpress.org/wp-share-buttons-analytics-by-getsocial/trunk@1025044 b8457f37-d9ea-0310-8a92-e5e31aec5664
remove old screenshots

git-svn-id: https://plugins.svn.wordpress.org/wp-share-buttons-analytics-by-getsocial/trunk@1025045 b8457f37-d9ea-0310-8a92-e5e31aec5664