DATAREST-384 - Fixed affordances and execution of sortable search resources.

Search resources are now considered sortable if they contain a Sort parameter. This is now reflected in MethodResourceMapping.isSortableResource().

Building on top of that, the RepositorySearchController now appends the sort template variable to links generated when listing search resources. It also now accepts resolved Sort instances to forward them to the query method execution. The controller now also uses DefaultedPageable so that request missing pagination information use the defaults configured for the PageableHandlerMethodArgumentResolver.