Starting to make stdout part of the handler contract

such that a given handler can change the payload before it is given to
the next handler.  Pipeline for real.
Inserting a payload annotator at the top of the pipeline

and starting to move some logic out of the rogue commit handler as a
result.
Moving watched branch decision to annotator
Adding a test for is_watched_branch annotation (whoops)
Merge pull request #42 from modcloth-labs/add-stdout-to-handler-contract

Starting to make stdout part of the handler contract