Initial version of bigquery backend.

First version of bigquery backend.

Lot of TODOs. But it should be good enough for anyone who wants to try
it out. Marked experimental.

Docker-DCO-1.1-Signed-off-by: Rohit Jnagal <jnagal@google.com> (github: rjnagal)
They are almost the same right now, except that bigquery doesn't do all the per_core ones. Cleaner way to do those would be to use a nested record, but I don't think we can do that in influxdb. We might want to push more data to bigquery than influxdb. So, we can't share schema but some of the column names can be same. I can make this work. I'll see how it looks when we have a decent schema done.