Batch Service Interface

This module provides an abstract class and interface and design pattern to make
it easier to write batch processing for Drupal 8 that leverage the service
injection system provided by Symfony.

Developers can create a service that can be used to generate and execute a
batch process that has easy access to translation, logging, and any other
services from the service container as needed.

It is meant both to be useful, and to encourage discussion of better ways to
support batches in Drupal 8 and beyond.