add onionoo version field to atlas/relay search

This is related to: https://trac.torproject.org/projects/tor/ticket/22488#comment:23

Goal: reduce the confusion for relay ops caused by false-positives of "you are running an outdated tor version" banner.

Below the platform field add the onionoo version field: https://metrics.torproject.org/onionoo.html#details_relay_version

Description: Version Tooltip text: Version of this relay as seen in the tor consensus

Based on the recent discussion on metrics-team ML I'm adding some ticket "metadata":

• This is a nice-to-have feature
• Would be nice to have it before 2019