New Gaul team bonus: reduce blacksmith tech cost.

The Gauls were part of well-connected trade networks in ancient times. Their exports mainly centered on slaves, mercenary, and military equipment.
As such, a team bonus reducing blacksmith costs makes much more sense than one reducing technology research time (particularly since the historical justification for the existing team bonus was... thin).

Patch by: Nescio

Approved by: borg-, ValihrAnt, wraitii

Differential Revision: https://code.wildfiregames.com/D2669