Changed UPS drain behavior, some balancing

* added USE_UPS_20 and USE_UPS_40 flags, which causes weapons to drain 20/12
and 40/24 UPS power per shot, respectively
* laser weapons now drain more UPS power (20/12 for pistols 40/24 for rifle)
* NO_AMMO and USE_UPS now both work correctly with burst-fire
* UPS energy drain now occurs inside the "shots" loop of game::fire in order
to drain the right amount of power during burst-fire