Redesign number of connected nodes viz

[bennlich]

Currently the number of connected nodes is rendered in sentence format at the top of the page:

It would be nice if this information was a little easier to parse. Maybe something like this sketch:

The circle size is proportional to node count, and the exitnode colors should match whatever we're currently using for the other plots (see: https://github.com/sudomesh/monitor/blob/master/public/js/exitnode-utils.js)

cc @haydenhw

[haydenhw]

Very cool! I've been busier with work lately but I hope to start chipping away at this soon!