True merchant underwriting

This PR updates the nbalanced code to hit the v1 balanced api with the proper inputs to actually underwrite as a business or a person so that it registers as a merchant in the balanced system.

Previously the nbalanced client simply created a new "plain" account when the Accounts.underwrite method was called.

This also adds the ability to underwrite an existing balanced account with merchant information and to validate embedded properties passed to the api.

Includes go-right tests.