Improve classic TR2 enemy randomization

- [ ] Offer cloning like TR1 - [ ] Lift skidoo and monk instance limits - [ ] Lift dragon limits (keep one per level, but remove workarounds for making textures fit) - [ ] Allow skidoos in HSH - [ ] Extend dropper enemy types (everything except eels) - [ ] Allow replacing required enemies (Ice Palace chicken and the OG dragon - HSH shotgun goon needs to remain for now)