update screenshots and improve widget behaviour in Customizer

git-svn-id: https://plugins.svn.wordpress.org/stock-ticker/trunk@1026021 b8457f37-d9ea-0310-8a92-e5e31aec5664
fix shortcode parameters glued bullet points on plugin description tab

git-svn-id: https://plugins.svn.wordpress.org/stock-ticker/trunk@1026022 b8457f37-d9ea-0310-8a92-e5e31aec5664