Tier 2 Howitzer

Adds a new upgrade to the Howitzer! Upgrade cost: 500 metal and 4000 energy Change Log: - Projectile damage increased to 750 - Device and Structure splash damage and radius increased to 1000 - Firing cost increased to 120 metal and 6500 energy - Recoil increased to 3,000,000 - Impact is increased to 300,000 - Hitpoints increased to 450 - Projectile health increased from 60 to 110 - Projectile size reduced to 60 - Weapon Mass increased from 180 to 600 - Fire angles increased to 0 through 85 degrees Also has a new sprite, courtesy of RoboRogue!