IconsCache.reloadIcon: Delete any bitmap cache file that cannot be parsed.
IconsCache: Reload all from the network if some part of the reloading fails.
Use some boolean instead of Boolean.
ItemsContentProvider: insert(): Refuse to insert without a subject ID.

It's not a real problem but it could be one day.
Add a final keyword.
ItemsContentProvider: Add *Downloaded boolean fields to mark when images are really fully downloaded.
ItemsContentProvider: addSubject(): Mark the image as downloaded, when downloading has finished.
ItemsContentProvider: queryItemNext(): Use a default sort order.

Actually, the caller already does this, but this is even safer.
List: Do not try to display an image if its data has not finished downloading.
SubjectFragment: Do not try to display the image if its data has not finished downloading.