Bigger smoke clouds for 105mm smoke rounds (Sherman 105 & StuH)

[Matt Hands]

Seems realistic that smoke rounds for 105mm howitzers would generate more smoke and a bigger effect that for 75mm rounds. Sherman 105 and StuH currently use same smoke rounds & effects as 75mm cannons.

I have added a DH_SmokeShellEffect_Large class in DH_Effects, which gives a smoke cloud that's about 50% bigger, so not OTT. Plus new smoke projectile classes for each 105mm-armed vehicle.

[Matt Hands]

Implemented in commit 3805a4a