Custom field detection. Minor fixes and improvements.

git-svn-id: https://plugins.svn.wordpress.org/video-thumbnails/trunk@862503 b8457f37-d9ea-0310-8a92-e5e31aec5664
Better Google Drive detection

git-svn-id: https://plugins.svn.wordpress.org/video-thumbnails/trunk@869386 b8457f37-d9ea-0310-8a92-e5e31aec5664