Asset picking has a few bugs with it

[darylhedley]

• Selecting the same asset for all three image sizes works fine but deleting one of them will not output the image at all in either the output folder or preview and removes the record in the courseassets collection
• When selecting or deselecting an asset it doesn't auto save on the object. This can cause the object to reference assets that are no longer attached to the course.
• We should really display some sort of visual reference to the asset instead of an input area