Add graph that compares total consensus weights across bandwidth authorities

We were talking today about how to compare bandwidth authorities, and make sure that different implementations are producing similar figures.

One easy way to compare bandwidth authority implementations is to compare their total bandwidth weights.

For example, this is the total bandwidth weight in the consensus:

$ cat Library/Application\ Support/TorBrowser-Data/Tor/cached-microdesc-consensus | grep "^w" | cut -d= -f2 | grep -v Unmeasured | paste -s -d + - | bc
43763163

Do you think we can do a graph of total bandwidth weight for votes? Should this go somewhere on metrics? Or should it be a once-off thing that Tom (or someone else) does?