Persist Job & batch information

[sammefford]

#612 asks that we persist JobReport. I'm thinking that would make a good cookbook example. We could persist at job start and update at job complete. I also like the idea of persisting per-batch details, like each uri and whether it succeeded or failed. I lean away from doing this by default as it adds some overhead. While the overhead would be minimal, it seems best if people add the listener explicitly to accept that overhead.

[sammefford]

Let's have this object allow setting of properties (similar to Map<String,String> that should persist with the job information. Also, let's allow setting the collections and WriteBatcher for persisting. Both should have reasonable defaults, such as a collection with the job id and creating an internal WriteBatcher so writes are asynchronous. To do this, however, the object will require a DatabaseClient passed to the constructor.