make SitemapPortletController auto-wire fail a runtime rather than init-time error

`SitemapPortletController` depends on rendering-pipeline-implementation-specific components such that its controller fails to init when the rendering pipeline is replaced with different components, breaking the portal build.  

This changeset makes the auto-wiring optional rather than required and detects the auto wiring failure at render-time, throwing an explicative `IllegalStateException` then.  This means that if you replace the rendering pipeline the sitemap portlet's dependency on the replaced components won't fail the portal build.