report api prototype

docs: https://docs.google.com/a/dimagi.com/document/d/1MFk_7cNXl4FYji3Q50AGGUx9VorrnARBuftCd_1gfVA/edit#heading=h.wuy47rvevj3

**Overview**
* Base class `ReportApiSource` provides methods to get meta data and results from config `dict` or `request`.
* `SqlReportApiSource` wraps `SqlData` - implementation feels a bit clunky
* Tastypie resource class `ReportResource` makes `ReportApiSource` class data available via HTTP.