Clear unusued cache

[cwoac]

As a user, I'd like to be able to clear out the files I no longer need from my cache

[bobpaul]

"No longer needed" as in "assets that no installed mods use?"

So am I correct this would be something like:

1. Loop through all mods and build a list of already downloaded assets for all installed mods.
2. Loop through the list of cached files and delete any that aren't referenced by a mod.