Add support for types in BigQuery

If you populate the 'type' field of a column using the type information BigQuery provides. It will help the UI with knowing how to better render stuff (like float vs. integer or datetime vs only date).

Currently there are no consts for this, so see here the list of types: https://github.com/EverythingMe/redash/blob/master/redash/data/query_runner_pg.py#L17