Use dpp-runner instead of babbage-fiscal

[akariv]

This is a bit thin, as most of the modifications were done in babbage.

The main change there is to support a slight change to the babbage model syntax for supporting joins between two DB tables.

It used to support a simple "join-column": "bla" syntax, allowing to join two db tables with the same name.
The change in openspending/babbage@53e20b6 extended that to a 2-string array, detailing the names of the two columns in the two tables.

[brew]

The babbage change still supports the single shared name syntax, as well as the new 2-string array, right? Looks good to me.

[akariv]

@brew I added what we discussed (removal of os-api-loader).
Please take a look!

[brew]

Cool, a couple of issues with old babbage fiscal imports.

I can't run this at the moment because of an import error for babbage_fiscal:
https://github.com/openspending/os-api/blob/feature/dpp-runner/os_api/cube_manager.py#L2

Similarly, tests are failing because of a failed import for babbage_fiscal:
https://github.com/openspending/os-api/blob/feature/dpp-runner/tests/conftest.py#L5

[akariv]

@brew tests are fixed now

[brew]

Great!

I'm having a little trouble getting the tests to run locally, as there are some additional moving parts -- installing some system dependencies, running dpp and setting env var (e.g. DPP_DB_ENGINE). Can you add these additional steps and settings to the README in the testing section?