Add support for integration tests

[lschaefer-sugarcrm]

Write an integration test for the Gradebook feature. See #38 (comment) for reasons why we're currently waiting to do this.

Once the test is written, ensure it can be successfully run as part of the Jenkins and Travis build processes.

[lschaefer-sugarcrm]

We now have several different use cases implemented, and we should revisit how we want to implement integration tests. All of our tests are currently at the unit test level.

@esimonetti has suggested using Postman for integration tests. The bonus here is that we already have the Postman infrastructure working and the tests are pretty straightforward and easy to understand.

@dwheeler brought up the integration tests at SugarCon, so I'm hoping he has some thoughts on how we should move forward. I'm guessing there is a reason that core Sugar has implemented their test infrastructure in the way they have, so we should be thoughtful and intentional if we are deviating from that.