There is now the possibility to download the transactions for all banks
in the banks table in the DB.
`NordigenInput` parse method fully functional, and entire chain from
downloading to parsing (simple w/ converter) to writing to DB.
DbTransaction type added __conform__ to simplify writes to DB.
Get bank methods added to both `Manager` and `DatabaseClient`.
Warning: csv parser most likely not working at this point.
Issues #16 and #17