Rewrite ScanDirector; improve its test.
Use Iterator for BatchIterator.flatMap.

This makes it convenient to use flatMap with standard collections in an efficient way. BatchIterator.batchFlatMap can be used with another BatchIterator.
Use BatchIterator through all of the examples.
Add a parameter for batch size to scan.

The changes over the past couple weeks now permit scans run in batches (or chunks) all the way from the replica up thru the stack to the HTTP client. That effort has paid off. Downloading the list of movies and actors runs 5x faster. Downloading the list of roles is now possible.

closes #76
Eliminate the Finatra project and library.

The project was created to house common code; the bulk of that common code has moved to the twitter-util and twitter-server libraries. Moreover, Finatra does not support HTTP chunking, and we want to discourage its use until it does.