Fix Rocket artillery

Rockets were high-intensity "shock and awe" barrages but suffered these drawbacks when compared to conventional artillery:
  • Long-reload times to prepare multiple barrels for next fast barrage
  • Time to move and redeploy because the rocket trails invited fast destruction from the enemy's counter-battery fire
Low ammo supply simulates both long reload time and time to redeploy within a hex.

The trade-off is high SA/HA for low ammo.

Possible New Rocket Units (besides the obvious nebelwerfers and katyushas: