Weapons selection improvements

[lemming104]

Relatively easy:

1. Add option to never change weapons on pickup, or at least never change weapons until player stops firing. This avoids the case where the player dies to a self-inflicted explosion if they stumble over a rocket launcher in the middle of a firefight.
2. Add option to prevent selection of weapons that are out of ammo and cannot fire.

More difficult:

1. Custom weapon preference/autoselect order