dataset_name__in filter not applied

[brlodi]

May be related to #177

When issuing a query against the /datasets endpoint, any provided dataset_name__in parameter (containing a list of dataset names to match against) is apparently ignored. For instance,

http://plenar.io/v1/api/datasets?dataset_name__in=311_service_requests_vacant_and_abandoned_building,311_service_requests_pot_holes_reported&obs_date__ge=2017-04-18&obs_date__le=2017-07-17&agg=day

returns 47 results not limited to the expected 2 datasets [transportation_department_permits, land_use_permits]. Removing the dataset_name__in parameter yields the same result.

The same parameter works as expected when applied to the /timeseries endpoint, eg:

http://plenar.io/v1/api/timeseries?dataset_name__in=311_service_requests_vacant_and_abandoned_building,311_service_requests_pot_holes_reported&obs_date__ge=2017-04-18&obs_date__le=2017-07-17&agg=day