Add CBM railgun and add penalty to CBM probability travel

CBM railgun doubles thrown range and damage of iron and steel objects. Thrown objects leave a trail of electricity like shocker zombies. Thrown iron and steel objects cost 1 power. Upkeep cost is a nominal 1 per 100 turns. Rarity was set to 5 and installation difficulty to 3. Grouped with ranged combat CBMs in mapitemsdef.cpp.

Balanced? I have no idea how good throwing is, or if it would be overpowered with double damage. The electricity trail doesn't really seem to do much (well, it *can* kill, but you'd probably have to miss 50 times to get enough electricity rolling around) but it looks cool :p.

Added a 10 energy penalty on failure to probability travel. Harsh, but probability travel can be an extremely powerful escape mechanism.