- nerfed base improved extraction rate for iron and horses from 2 to 1

All strategic resources now have an improved extraction rate through techs:
- Horse (Base: 2), +1 with Horseback Riding, +1 with Stirrups
- Iron (Base: 2), +1 with Apprenticeship, +1 with Metal Casting, +1 with Industrialization
- Niter (Base: 2), +2 with Scientific Theory, +2 with Chemistry
- Coal (Base: 2), +2 with Steel, +2 with Steam Power
- Aluminum (Base: 2), +2 with Rocketry, +2 with Lasers
- Oil (Base: 3), +2 with Plastics, +2 with Synthetic Materials
- Uranium (Base: 2), +2 with Nuclear Fission, +2 with Nuclear Fusion