Export to NF-e, the client role (Individual/Company) according to registered document

- Verify if document(CPF/CNPJ) exists.
- If both documents are registered on the same client, export only CPF.
- If there is no document registered, export the client as Individual
with blank CPF.
- Improve tests.

Change-Id: Ifd0684633b15d5035ba5c4b1ba706dd22a1e2e15