Reworked AT gun ammo capacities and resupply intervals

[GDrukenmiller]

• Decreased initial ammo by roughly 20-25% for all guns to better match quantities realistically carried by gun crews.
• Decreased maximum capacities by 50-60% (there is really no reason at all for a Pak 40 to be able to stock up nearly 100 shells, especially when this is stacked on top of ammo crates, giving effectively infinite ammo).
• Set custom resupply intervals for most AT guns. On average, interval is now 1.75x the reload speed of the gun. This is intended to reduce the usefulness of spam firing, as you will now end up firing faster than shells can be replenished.
• Decreased the rate of fire on a few guns, namely Pak 38, Pak 40 and Zis 3. Reload times were increased by .25 seconds. Still faster than any tank cannon, but overtime slightly reduces the "machine gun" effect these guns currently have.