Deal better with deleted videos

* Created setting to remove/keep posts when removed on remote site as
  per patch by Dan Baritchi
* Instead of removing posts, they now end up in the trash
* Added post_excerpt storage, used by some sites

git-svn-id: https://plugins.svn.wordpress.org/external-videos/trunk@842197 b8457f37-d9ea-0310-8a92-e5e31aec5664