Added Plupload feature from Image Content Block. Now the content block uploads when a file is dropped.

git-svn-id: https://plugins.svn.wordpress.org/wp-content-blocks/trunk@855999 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated plugin with Image and Gallery Content Blocks working, and initial state for Audio / Video Content Blocks (with oembed support).

git-svn-id: https://plugins.svn.wordpress.org/wp-content-blocks/trunk@859536 b8457f37-d9ea-0310-8a92-e5e31aec5664