RadiationMapsMaker: added switch to simulate upper hemisphere only

The switch PositiveYOnly is needed to restrict the radiation maps to the upper hemisphere (y>0) which allows to get radiation estimates in the shafts to the cavern all the way up to the surface about 90 m above the IP. Below y = -20 m the world volume ends and averaging in phi would fail if this region would not be excluded. The new flag is needed also for Phase-I (21.3), Phase-II (21.9) and master.