Fixed an error

Removed iron cost for crossbows, quadrireme, catapult.
Increased cost of caravel, frigate and privateer to 10 iron (up from 5)
Increased swordsmen cost back to 20 (the base game value)
Changed production cost of biplane from 10 oil to 10 niter
Changed production cost of helicopter from 10 aluminium to 10 niter
Increased horses from horse pastures from 2/turn to 3/turn
Increased niter from niter mines from 2/turn to 3/turn
Reduced uranium cost of nuke and thermonuke back to 10/20 (the base game values)
Fixed an error where the nuclear submarine did not require uranium

Nuclear submarine: because this is the only unit (except the giant robot) that consumes uranium, I've tweaked the stats a bit to compensate: movement increased from 4 to 6, and maintenance reduced from 8 to 7.

Added resource costs for five units from the Steel and Thunder mod: Galleas, Gatling Gun, Mortar, Rifleman, Self-propelled Artillery