Add/Edit Distribution Preference

- when a distribution preference is created or updated, make sure it is immediately visible on the related subparts and classes
  - this fixes a problem introduced in commit 0885742 which made the PreferenceGroup.distributionObjects no longer updated

JavaSource/org/unitime/timetable/action/DistributionPrefsAction.java

@@ -709,6 +709,7 @@ else if (owningDept.getDistributionPrefPriority().intValue()==clazz.getManagingD
             	dObj.setDistributionPref(dp);
             	dp.addToDistributionObjects(dObj);
             	hibSession.persist(dObj);
+            	dObj.getPrefGroup().addToDistributionObjects(dObj);
         	}
 
      	    sessionContext.checkPermission(dp, Right.DistributionPreferenceEdit);