=pro Add akka-http to the aggregate project

and fix 2.11 dependency
akka-http itself wouldn't really need a dep on scala xml.
However, we do provide default (un)marshallers to and from `NodeSeq` (e.g. [here](https://github.com/akka/akka/blob/release-2.3-dev/akka-http/src/main/scala/akka/http/unmarshalling/PredefinedFromEntityUnmarshallers.scala#L46), and because these currently live in companion-object-implicit-scope we do have a dependency.

What we could/should do:
Move the (un)marshallers for `NodeSeq` out into a dedicated trait/object and switch the dependency to `provided` scope.