add consensus weight line/graph

Relay Search has two graphs showing bw history data and relative values (fraction and probabilities):

• consensus weight fraction
• middle probability
• guard probability
• exit probability
• written bytes per second
• read bytes per second

One of the most relevant question for a relay operator is: How is my relay doing? Is it doing better or worse than usually?

A good data point to answer this is to look at the cw value over time (not cw fraction) since the probabilities and fraction values are relative and not directly controllable by the operator (i.e. other operators add relays).

This will allow relay operators to answer questions like: "My cw fraction decreased, was it because my cw decreased or did my cw remain stable and someone else added more resources?"

a graph showing the ratio between cw fraction to cw would also be nice since it answers above question more directly without having to compare the cw and cw fraction lines manually

onionoo data: https://metrics.torproject.org/onionoo.html#weights_relay_consensus_weight

the onion box displays a cw graph: https://raw.githubusercontent.com/ralphwetzel/theonionbox/master/docs/images/weights.png