Let players (and AI) toggle ambush on Units

Stealth units right now are in a very weird state with diplomats, since diplomats run through territory constantly risking ambushes with every move. An easy way to solve this issue would be to toggle ambushes on or off for specific armies, and for each ambush ignored simply giving the unit a detection penalty depending on how many units were in the army that would have been ambushed. This also makes spies less useless, because right now its nigh impossible for a lone agent to finish an action before a random unit stumbles upon it. If a player wanted to use their agent for espionage they should be allowed to toggle ambushing on that unit off. This would also lead to a lot less random ambushing grievances from the AI, which tend to give the player an unfair edge through unearned war support.