Bug 1028691 - [Collection app] Background images sometimes in poor quality

http://bugzil.la/1028691

Since the collection.background can be updated by two processes - a) Collection create b) Collection view, the former requests a 170x170 image which is then displayed as the Collection content bg. Then gets overwritten with the full size bg.

The fix simply keeps a record if the current bg image is full sized or not and displays only if it is.