Builder huts upgrade

Lv. 2 = Hitpoints 300, and 3% faster build, cost:230 000 gold, unlock th5 Lv. 3 = Hitpoints 380, and 7% faster build, cost:650 000 gold, unlock th6 Lv. 4 = Hitpoints 520, and 10% faster build, cost:1 700 000 gold, unlock th8 Lv. 5(max) = Hitpoints 650, and 15% faster build, cost: 3 100 000, unlock th10