VramTestActor: Fixed missing getSettingsID causing load actor from file to load vram actor instead.

The missing getSettingsID() override in the MVramTestActor caused some actors, when loaded from file, to be created as a MVramTestActor. This was caused, because MActor provides a default implementation of getSettingsID(), which is needed. However, any actor needs to override that function, so that its actor factory can recognize an actor config file to be of that actor. If the function is not overridden, the factory accepts all MActor subtypes.

The getSettingsID() function was made pure virtual in MActor to avoid this issue in the future. It still has a default implementation in MActor though.