3.7 Samurai upgrade track

Samurai & crossbows both upgrade to Gatling guns. Also, Gatling guns need iron. Not sure if the latter is an intentional change.

Found this change also affected Longswordsmen (so consequently warriors & swordsman too). Corrected it by removing Line 32

UPDATE Unit_ClassUpgrades SET UnitClassType = 'UNITCLASS_GATLINGGUN' Where UnitType IN (SELECT Type FROM Units WHERE Class = 'UNITCLASS_LONGSWORDSMAN');

from the CEA_Start file.