Add a "Make Permanent" action for the manage files listing

Description of the need I just ran into an issue where I wanted to manually mark a bunch of temporary files as permanent, but the only way I could do that was with a database query. I'd love to have a bulk operation instead.

Proposed solution Add an action for the drop-down on the files listing at admin/content/files

Additional information I don't think we need to provide the opposite (make temporary) because most people would probably delete that file if it were not wanted.