DefaultContentBeansTool.getAnnotatedClasses() doesn't need to depend on HstRequestContext

Currently, DefaultContentBeansTool.getAnnotatedClasses(ClasspathResourceScanner) depends on HstRequestContext only because it wants to read servlet context parameter.

It must be more useful to let it not depend on HstRequestContext. It can access ComponentManager#getServletContext() instead.

This will make it more convenient if someone wants to create an ObjectConverter where there's no HstRequestContext available. e.g, an hippo event listener implementation.