Added "Downloaded" category to Addons menu
* This lists ALL locally downloaded workshop items that are not currently subscribed to, such as those from server downloads (WorkshopDL) and steamworks.DownloadUGC
* It also (unfortunately) appears to contain downloads for other Steam users on the same PC
* You are able to mark stuff unused from the menu without having to wait for 2 weeks to for Steam to automatically delete the server downloaded content