Add DLC for games you already own

[MrLabRat]

Just an idea as a quality-of-life feature. As cloud saves aren't working with games added through the unlocker, even with games you own, adding a Lua file into the tool with the DLC AppIDs added and will add all the DLC there while still retaining cloud save support—so if there was an option to just add DLC instead through the unlocker, it'd be better than having to mess around with .lua files.