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
Initial view
Response to CR
Template changes
Response to CR
More response to CR
CR response
Response to CR 1-13
Response to CR 1-14
Final iteration
Merge pull request #1888 from edx/flowerhack/feature/certificate-revenue-reporting

Verified Certificate Reports