+ Makes reusing flows safe
+ Adds timerTransform for ops which need TimerTransformer
+ Adds TransformerLike in order to keep transform/timerTransform
typesafe in respect to the passed in type og Transformer
Resolves#15271
* implicit param
* change tests to use implicit materializer
* add ActorFlow trait that provides an implicit materializer inside an actor
in the right way, i.e. encourage usage of that instead of
implicit def mat(implicit arf: ActorRef): FlowMaterializer
* make http compile, but those who know the api better will have to adjust
to take full advantage of the implicit materializer
