Feature: maxViewDistance, maxViewDistanceAtDark moved into ruleset

* maxViewDistance, maxViewDistanceAtDark and maxDarknessToSeeUnits moved into ruleset. Feature request 232 -Unlimited view distance: http://openxcom.org/bugs/openxcom/issues/232
* optimization of TileEngine::visible()

Upd:
before optimization 410 FPS
after optimization 460-470 FPS
:P