1-handed / 2-handed mode should be enabled for most firearms

[FWolfe]

This will require extra animations (for build 41) but many (if not all) firearms should allow for switching stances, modifying weapon stats per stance.
Even rifles and shotguns should be able to fire single handed with massive penalties. Current PZ engine mechanics for weapons that can be used 1 and 2 handed suffer a damage reduction when used 1 handed (java hardcoded).
A new system will need to be put in place that simulates 1h/2h usage by toggling if a weapon is 2h required, and adjusting hit chances and other stats on switch