When confirm a sale, select the batch if is unique

- If sale item has only one batch, auto select the batch to confirm the
sale.
Previously, we needed open a new wizard to select the batch, now this
wizard will be opened only if the product has more one batch.
- Add tests.

Change-Id: I48500ba6077b1d37edb513d2cc4c05e581f78cb7
Fixes: http://bugs.async.com.br/show_bug.cgi?id=5639