Add tributary logic to maestro

1) extended tributary logic by avoiding copying duplicate files
2) refactored tributary logic so it is an Hdfs action
3) fixed tributary logic so that archive directory structure mimics HDFS source structure
4) changed tributary tests so they each run in an isolated directory
5) date parsing does not allow overflowed days and months
6) many other misc changes to tributary logic

Sorry about the size of the pull request :(
Well, it doesn't continue with the flow. But the caller doesn't get any return type indicating the flow wasn't set up properly, and they should do. Part of reconsidering the flow API should be thinking of a suitable return type.