combine the examples projects into one

Let's merge wicket-spring-examples, wicket-spring-annot-examples (1.x only) and wicket-auth-roles examples into the wicket-examples project so that we have less work to do when releasing, and we have one project where people can find all information. We have to evaluate whether wicket-portlet-examples is release ready, and whether we want to keep supporting wicket-spring-cattr-(examples).