Add ability to create and submit Steelbrick Contract to Zuora via API

[grayjoa]

It would be great to have the ability to have a Salesforce CPQ quote contracted using an automated process. Currently the code to create the billing account in Zuora when the quote is contracted is not exposed. If this could be exposed to automate this process this would be very helpful to save manual steps during the quoting process.

[nathanc]

Will try and get this into 2.7