[Update] Megapack

The usual ZScript and PK3 conversions, with the Uberpack giving a higher increase in ammo capacity than a normal backpack, I felt that the Uberpack's function of giving max ammo I feel would work well with the Megapack instead so it's more unique, the infinite ammo powerup has been dropped to 30 seconds to compensate for instant max ammo, it still gives a normal backback upon pickup. Given the description states that it has a bit of demonic powers, I added a small red skull on it to further sell that fact...and the fact I felt it was pretty sharp.