Prototype of FlowGraph

Early prototype for discussing the way forward.
Before we start with the DSL sugar I would like that we express the functionality in terms of something similar to the raw addEdge methods.
Is that really depth first? You mean breadth first.
That is not supported from multipe starting points at the same time with the built in traversal in the graph library, as far as I know.

How does your api in the flow materializer look like?