Provide helper class for breadth-first traversals with cycle check

[kbirken]

We are using breadth-first-traversals of structures (ASTs, POJO graphs, ...) in various locations of our code. A configurable, flexible traversal helper should be provided which can be used in those places instead of re-implementing the worklist/while/visited-algorithm again and again.

The helper should provide two APIs:

• an API with static methods for doing simple traversals as "one liners"
• an API as abstract class for doing more complex traversals

[kbirken]

PR has been merged successfully, closing.