This entails:
* adding akka.pattern.PatternCS.* to enable ask etc. with
CompletionStage
* changing RequestContext to offer an ExecutionContextExecutor for the
CompletionStage.*Async combinators
* splitting up akka.stream.Queue for JavaDSL consistency
* make the standard queries "single method interfaces" that may be implemented
by a query journal plugin
* remove hints (major problems with varargs anyway), the hints for standard
queries should be given in configuration instead, e.g. refresh-interval