Option for editing buttons to choose if a new empty feature should be added to the model when editing is finished

In MapBuilder 1.0.x, editing widgets (EditPoint, EditLine, EditPolygon) could only be used to create a single feature. In MapBuilder 1.5rc1, this behaviour changed: Now after creating a feature, a new empty feature will be added to the model. If a users wants to have the MapBuilder 1.0 behaviour, she can now use the <appendOnEdit>false</appendOnEdit> property of the editing widgets to do so.