Moved plugin screenshots to assets folder.

git-svn-id: https://plugins.svn.wordpress.org/pinterest-verify/trunk@845471 b8457f37-d9ea-0310-8a92-e5e31aec5664
Moved plugin screenshots back to trunk.

git-svn-id: https://plugins.svn.wordpress.org/pinterest-verify/trunk@845472 b8457f37-d9ea-0310-8a92-e5e31aec5664