Add min & max engagement altitudes for ww2 searchlights

[Night Owl]

Earlier this year, an option to set the min and max engament altitudes has been added to ww2 AAA units. This is very helpful for fine tuning the air defense unit's behaviour to make it more realistic. I am therefore asking if the same option could also be added for the searchlights (Flakscheinwerfer 37). Searchlights were used primarily for guiding heavy flak and night fighters for the defense against night bombing raids. They would not have been able to track single fighters flying fast on the deck. Thus, having a min engagement altitude option for them would enable us to make more interesting and realistic night missions. For example a low level Mosquito raid flying past the flak and searchlight emplacements deep into enemy lines.