Adds support for /api/v2, the sdk api at the surface level should be unchanged, but then underlying structure has gone through some large changes.
RemoteDataset is now an abstract class with implementations for both v1 and v2 datasets, clients picks the right implementation depending on payload.
Client also has a new .api_v2 field, that contains all backend calls to /api/v2, I would like to do the same for v1 but it's possible that past users are depending on tho
se calls existing inside client which makes this a bit tricky.