[QuickMods] Redoing how QuickMod files are downloaded and stored, both on-disk and in-memory

This is still WIP, and mainly for me to keep track of what needs to be done.

- [x] Get rid of QuickModFilesUpdater
- [x] Rename QuickMod to QuickModMetadata, and remove versions from it
- [ ] Make QuickMod*Refs way thinner
- [ ] Change how QuickMods are saved in memory
- [ ] Change how QuickMods are saved on disk
- [ ] Make sure everything still works