Set the generators on loaded worlds

- uses reflection to access private fields of CBS internals
- sets the generator correctly (verified)
- sets the populators correctly (verified)
- should also work for augmented world types (needs verification)

PlotSquared/src/main/java/com/intellectualcrafters/plot/PlotSquared.java

@@ -498,6 +498,7 @@ public class PlotSquared {
     }
 
     public PlotSquared(final IPlotMain imp_class) {
+        SetupUtils.generators = new HashMap<>();
         THIS = this;
         IMP = imp_class;
         try {