Create BulkAddBatch and use it for bulk add

This lets us add a second subclass for the ImportBatch which will have
different inputs and behaviour.
BulkAddBatch should create BulkAddBatchEntries
Basic ImportBatch#create_entries
Add ImportBatchRow

This will represent a row in the import CSV/TSV. It will act like a presenter,
encapsulating knowledge of how to translate the row into a ImportBatchEntry.
Add a basic ImportBatchesController