code: public void registerPlugin(final DajlabExtension plugin) {
  
  		if (plugin != null) {
  			if (plugin instanceof DajlabControllerExtensionInterface) {
  				controllers.add((DajlabControllerExtensionInterface<DajlabModelInterface>) plugin);
  			}
  			if (plugin instanceof TabExtensionInterface) {
  				tabPlugins.add((TabExtensionInterface) plugin);
  			}
  			if (plugin instanceof MenuExtensionInterface) {
  				menuPlugins.add((MenuExtensionInterface) plugin);
  			}
  		}
  	}
docs: Register an extension. Should be called in the constructor method of the
  implemented class.
  
  @param plugin
  the extension to register.