Balance H&K G3 rifle

[Xenonauts]

I think the G3 rifle is a bit too strong in comparison to other rifles so we have to add some cons to make the usage of other rifles more reasonable.

My suggestions are:

• to increase the TU costs for every fire mode (the costs should lie between that of the standard assault rifle and the sniper rifle (G3 SG/1)
• to reduce the reaction fire modifier e.g from 1.0 to 0.8, as this weapons is larger and heavier than the M16