Correct duplication of GameObjects

[JamesTKhan]

When you duplicate a GameObject in the editor, each component is cloned in GameObject.java

        this.components = new Array<Component>();
        for (Component c : gameObject.components) {
            this.components.add(c.clone(this));
        }

However, some components do not have cloning implemented due to technical limitations or just not being implemented yet, like terrain component

    @Override
    public Component clone(GameObject go) {
        // Cant be cloned right now
        return null;
    }

When duplicating a GameObject with components that cannot be cloned the editor crashes as a null component gets created and a NPE happens. We should add logic to handle when a null component is returned, either stop cloning the game object, or clone it partially without the components that could not be cloned. Adding a UI dialog in the editor would be a nice addition as well to notify when this happens.

[JamesTKhan]

Closing this out as I have disabled the duplication button for Terrain and Water components in UI, as well as throwing an exception on cloning of Water or Terrain as cloning them is not supported.