Add InfoRequestBatch model.

Re-annotate models.
Use two bodies in specs.
Simple code for the happy path

Create the batch and associate new requests with it, send the outgoing
messages, and redirect to a page for the new batch.
Make method names for finding existing objects clearer

They're not finding by the existing object, they're finding an existing
object.
Add check for double submission.
Notices for success and errors.