Nerf Iberian fireships as they are much cheaper than garrisoned WarShips, easier to spam and destroy docks 5 times faster.

Double decay rate, so that the lifespan becomes 1min 23sec instead of the original 2min 46sec.
Increase train time form 20 to 30.
Increase cost from 200 wood to 300.

Differential Revision: https://code.wildfiregames.com/D388
Numbers By: Hannibal_Barca
Reviewed By: fatherbushido
Discussed with: causative, Grugnas and scythetwirler