CDAP-540: Ported RecommendMovieProcedure to MovieRecommendService.

Implemented the MovieRecommendService in according to the RecommendMovieProcedure.
Old implementation is still available to compatibility with current user guides.
The `scan()` method returns `CloseableIterator`. You need to close after used.

CloseableIterator<...> userRatings = ...;
try {
  if (!userRatings.hasNext()) {
    ...
  }
  CloseableIterator<...> userPredictions = ...;
  try {
  } finaly {
    userPredictions.close();
  }
} finally {
  userRatings.close();
}