Feature: Show the probability of hitting

Improvement of the "rangeBaseAccuration" option:
- is taken into account density of smoke between shooter and target;
- is taken into account visibility of target unit.

Added option "showChanceToHit":
![screen017](https://f.cloud.github.com/assets/3616568/917185/4d1bcb58-fe9f-11e2-84ac-65bf76b3ddae.png)
![screen055](https://f.cloud.github.com/assets/3616568/917199/74b84c04-fe9f-11e2-85d2-2c107b996157.png)