Include BurstFiringRate for Fire Rate of burst weapons

[tsakistan]

The formula for calculating the fire rate of burst weapons as shown on the stat card is:
CartridgePerFire / ((CartridgePerFire-1) * 1/BurstFiringRate + 1/FiringRate)

The only stat missing from BBA export is BurstFiringRate

Example:
Sunbeam Bundlebuss shows fire rate 6 in game.
From RangedWeapon.json:

FiringRate: 1.017,
BurstFiringRate: 20,
CartridgePerFire: 8
8 / ((8-1) * 1/20 + 1/1.017) = 6