code: @SuppressWarnings("rawtypes")
  	public <FROM, TO> void addDependecy(FROM from, PropertyUpdater<FROM, TO, T> updater, TO to) {
  		PropertyInterface fromProperty = Keys.getProperty(from);
  		if (!propertyUpdater.containsKey(fromProperty)) {
  			propertyUpdater.put(fromProperty, new HashMap<PropertyInterface, PropertyUpdater>());
  		}
  		PropertyInterface toProperty = Keys.getProperty(to);
  		propertyUpdater.get(fromProperty).put(toProperty, updater);
  		addDependecy(from, to);
  	}
docs: Declares that if the key or property <i>from</i> changes the specified
  updater should be called and after its return the <i>to</i> key or property
  could have changed.<p>
  
  This is used if there is a more complex relation between two fields.
  
  @param <FROM> the type (class) of the fromKey / field
  @param <TO> the type (class) of the toKey / field
  @param from the field triggering the update
  @param updater the updater doing the change of the to field
  @param to the changed field by the updater