Adds model classes for credit cards.
Adds credit card transactions for Swedbank and Sparbankerna. Fixes #339 and #332
Merge pull request #344 from goober/feature/332-swedbank-credit-card-zero-balance

332 swedbank credit card zero balance
New certificate for CSN. Fixes #346.
Merge pull request #347 from auno/346-csn-certificate-not-trusted

New certificate for CSN