Please include unique voters in GR graphs

[Niels Thykier <niels@thykier.net>]

Hi,

It seems that GR has a stats/graph page like this:
 * https://vote.debian.org/~secretary/gr_initsystems/ (ongoing)
 * https://www.debian.org/vote/2019/suppl_001_stats (finished)

This includes a graph over ballots received, votes tallied etc. over
time.  I would like to see the number of unique votes as well.  The
unique voters count is interesting because it reflects our voter turnout.

Related, assuming the script knows the number of eligible voters, having
the current actual voter turnout would be great too.

Thanks,
~Niels