refactored the payment_method api with tests and doc
Merge branch 'master' of github.com:fritzpay/paymentd into project_method_refac

Conflicts:
	pkg/paymentd/payment_method/sql.go
	pkg/paymentd/payment_method/sql_test.go
	pkg/service/api/v1/payment_method.go
fixed test
Merge pull request #79 from chruffer/project_method_refac

Project method refac