Add per-relay descriptor timestamps to the consensus health detailed page

There seems to be a bug where directory authorities take a while to update relays' Tor versions: https://lists.torproject.org/pipermail/tor-dev/2018-January/012786.html

In the Overlap table, let's mark versions as "In Vote And Consensus" if the vote matches the consensus, "Only In Vote" if the version is present and does not match the consensus, and "Only In Consensus" if the version does not match the consensus.

Unfortunately, consensus-health does not load descriptors, so we can't check the actual version reported by the relay.