Initial PR for verified cert reporting

Refactored from code in Stanford's itemized revenue reports into a new Report class used for all revenue-related reporting.

Models for all cert types complete; test coverage for half of cert types complete.

If this architecture is deemed solid, the next steps are to add a reasonable UI folks will use to select reports to download, allow them to restrict based on dates/universities, and of course complete test coverage.
Fixed CertificateStatusReportModel
Fixed UniversityRevenueShare model
Refactored tests
Migrations