I installed the plugin as described in the instructions, including renaming the plugin directory to "menu_builder." Added it to the $helpers array as MenuBuilder.MenuBuilder, and constructed the beforeFilter array pretty much as described in the instructions. Added it to my default layout as described, and I get fatal error: Error: An Internal Error Has Occurred. Helper class MenuBuilderHelper could not be found. The only helper class in the plugin that I can find is MenuRendererHelper. What do I need to do to make it work?