Add OONI's Vanilla Tor measurement data to Tor Metrics

OONI has a test called Vanilla Tor which "attempts to start a connection to the Tor network. If the test successfully bootstraps a connection within a predefined amount of seconds (300 by default), then Tor is considered to be reachable from the vantage point of the user. But if the test does not manage to establish a connection, then the Tor network is likely blocked within the tested network."

We should get these measurements into Tor Metrics.

I spent the last couple days on downloading a copy of the OONI metadata database and extracting useful data from it. I'll add some results after the lunch break.