Allows us to call tests on things other than python3, with the same settings.

For uniformity with the indexer-storage.

This simplifies the Docker entrypoint (it can just call 'initialize'
unconditionally); and allows easy addition of new fields to an index.

Field removal would still need to be done manually.

Origins are no longer dicts.

The journal client now uses Consumer.consume instead of Consumer.poll,
so not mocking Consumer.consume resulted in infinite loops.

thanks @vlorentz for pairing with me for this!

This also adds a 'has_visits' boolean field to origin documents,
which will be set to True as soon as a visit for the origin is
seen.

'cursor' has a different meaning in our components using postgresql;
this renaming will avoid confusion when adding token-based pagination
to these components.

It keeps failing and I don't know what it is.

Related D2082

For some reason tests pass when run out of tox.