Client for stream download of analysis datasets

[rafatower]

Add client code for stream downloading of datasets from analysis/enrichment

result = Dataset.name(‘my_dataset’).download_stream()
df = pd.read_csv(result)

(there should probably be also a wrapper to stream to a CSV file on disk).

See DO API v1.0, Download and https://github.com/CartoDB/data-observatory/issues/594

[rafatower]

Superseded by https://app.clubhouse.io/cartoteam/story/56013/client-for-stream-download-of-bq-datasets