Torch and shield usage inconsistent with original game

1. I can be wrong, but in my testing NPC hide torches during rainy weather in original game. OpenMW does not have this behaviour - we check only for darkness (isDark() function).

2. Shield, torch and two-handed weapon equipping is inconsistent too. In original game, when you equip shield or torch, an engine force you to unequp two-handed weapons. When you equip two-handed weapons, an engine forces you to unequip torch, but not shield (IIRC, MCP fixes shield bug-feature). In OpenMW, an engine allows you to equip light sources and shields with two-handed weapons. From the other hand, we have a hack in Actors::updateEquippedLight() to emulate vanilla behaviour for NPCs, but it does not well: during combat NPC will have both weapon and torch equipped, so the torch will be visible during weapon unequipping animation (another difference from Morrowind).

The simpliest way to fix 2. is to make equipping differences togglable at least.

(RM-4334 from redmine: created on 2018-03-01 by Andrei Kortunov, , closed on 2018-03-21 by Andrei Kortunov)