flowdetails meta is not visible publicly from the engine

We have need to get at the flowdetails 'meta' field from objects that only have access to engine.storage. We *can* do engine.storage._flowdetail.meta to get it, but relying on a private attribute seems problematic. I propose that the Storage object should expose the underlying flowdetail object as a public attribute.

@property
def flowdetail(self):
    return self._flowdetail