=str #16001 Propagate error to FoldSink's future

* align OnCompleteSink's implementation of error/success handling with
  that of other Sink's
Merge pull request #16006 from volkerstampa/wip-16001-foldsink-error-handling-volkerstampa

Propagate error to FoldSink's future. Fixes #16001
!str #15977 Rename and change types in the new DSL

* Cleaned up type signatures
* Changed names of Source/Sink/ProcessorFlow to Tap/Drain/Pipe
* Introduced new Source/Sink/Flow
* Made all Pipe types package private
* Changed the TypeGraph DSL to work on Flow/Sink/Source
+hco #15798 add missing java api for Connection.tokens

Resolves #15798
Merge pull request #16024 from ktoso/wip-hco-java-api-connection-ktoso

+hco #15798 add missing java api for Connection.tokens
Merge pull request #16007 from akka/wip-15977-changin-all-the-small-dsl-things-ban

+str #15977 Rename and change types in the new DSL
=str #15874 Hook-up balance operation