Add CBM Chain Lightning and related ammo effects

Added chain lightning, implemented as a weapon (like the fusion blaster) doing 6 damage (pretty much always a headshot because of high accuracy in testing), leaving a trail of, and causing a radius 1 explosion of fd_electricity, and bouncing to a nearby monster target within 4 tiles of the previous target. Lightning will only hit a target once and bounces up to 10 times.

Added AMMO_LIGHTNING flag, which causes ammo to leave a trail of lightning and cause a radius 1 explosion of lightning. Also added AMMO_BOUNCE flag, but you shouldn't use AMMO_BOUNCE for modding because it a) takes no time to fire (imbalanced), and b) consumes weapon charges for each bounce (makes no sense regular weapons... well, maybe for a lightning gun), and will continue to bounce until you're out of ammo or targets. Neither were issues as a bionic, but probably wouldn't work well in modded ammo.