support "async" / non-blocking queries #17
Description
Follow-up to googleapis/python-bigquery#1182 and internal issue b/155989404.
In many cases, the query in the notebook may take a long time. It would be useful to be able to return a "future" object that can print out the job information in the notebook. This would allow the cell to return quickly and not block the user from using the notebook for other work in the meantime.