Adds ability to use a unique ID per set of credentials

Would close #218 if merged.

This PR also includes a refactoring of the code that interacts with waltzio/cy in waltzio/waltz.

Right now, this generates a 13 character ID like `clxb39578ehfr` and uses that to get a new key from waltzio/cy.

Possible changes we could make:

* append the siteKey to the beginning, so the credentialID that waltzio/cy would see would be like `facebook_ clxb39578ehfr`