Add total number of parties to heatmap

This PR adds the total number of parties known using the `/event-stats` route already added and a HTML overlay w/ some absolute positioning relative to the heatmap.

The total will only show on a successful loading of the heatmap itself.

Implementation based on this design <https://www.dropbox.com/s/oipryxnofxtnp3h/makerparty_liveupdates_idea2updated.png>