Add DeclaredServletContainerInitializer

[mnriem]

As per the Servlet specification one needs to limit access to certain Servlet APIs when the web.xml, the web-fragment.xml files and the Servlet annotations have been processed. Currently this happens as a side effect during the processing of the Servlet annotations done by its extension. To make it clear when this state change happens this issue will pull out the functionality into its own WebApplication extension.