Implement Add switch for armor degradation fix. #6888

Implements #6888 (closed).

Adds a Game setting "unarmed creature attacks damage armor" (by default false, corresponding to how it is in Morrowind.exe) and a simple setting condition check. If the setting is enabled, unarmed create attacks reduce armor condition, just as NPC attacks and armed creature attacks.

Adds the setting to the default settings template, to the launcher (Advanced -> Game Mechanics tab) and to the documentation.