Limit missile silos

This mod limits missile silos to a maximum of 2 each. I.e. you can only place 2 normal swarms or 2 warheads and 2 swarms or 2 inverted warheads, 2 warheads, 2 inverted swarms and 2 swarms. I cannot set a common limit, a limit to a maximum of 3 missile class weapons is not possible (to my knowledge). COPYING INFO: Since this is a very small mod, copying/modifying any part of this mod is allowed.