by aaron: Copy the sample image to the public:// folder for image style previews, due to bug at [#987846].

by aaron: Ensure we don't create duplicate styles when saving, and delete duplicate entries from the styles table in an update.

#1017770 by aaron: Fix the update process was aborted prematurely while running update #7208 in styles.module.

#984018 by das-peter, aaron: Fix effect link_to_media not found for thumbnail display formatter style of the FileStyles class.