Improved Civilian fleeing mechanic

[MiC17]

We've done a lot of talking about this already and that has made it clear how big of a task it is to create believable behaviour for non-combatants.
I've split the problem into two (for now) manageable chunks, the smaller one of which this suggestion describes.

Basically what this does is: replace the current fleeing mechanic (aka. headless chicken) with one of the following two responses to "shots fired in the vicinity".

1.) Civilian checks his surroundings for hiding spots (building positions), picks one (as close as possible), goes there and crouches or lies down. He then stays there until at least 15 minutes after the situation has cleared (maybe disable AI entirely for that time). Should be clear what existing code this utilizes. ;)

2.) In a certain amount of cases (maybe 20%) or if failing to detect a hiding spot in 1. (because there's no building closer than 100m meters for example) the Civilian will instead go prone and shut down until at least 15 minutes after the situation has cleared.

Bonus feature:
After 1. or 2. has been executed the Civilian automatically becomes a hostage, enabling players to evacuate Civis out of an area, if they choose to do so.