move banner to asset

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-sample/trunk@886379 b8457f37-d9ea-0310-8a92-e5e31aec5664
move screenshot to asset

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-sample/trunk@886380 b8457f37-d9ea-0310-8a92-e5e31aec5664