Network Visualization for Agents on the Network Nodes

[DrTao]

What's the problem this feature will solve?
It looks as though the current Network Visualization shows the base network but cannot show the agents.

Describe the solution you'd like
I'd developed a workable extension for Swarm (GeoGraphs) a while back that solved this nicely.

We showed agents as circles smaller than the nodes (relative radii are parms), where each agent's pos=(x,y) was centered on the node's center and then each agent's pos varied by a specified radius and tiny random scatter so they were not all right on top of one another. We also allowed different colors/types of agents to display at different quadrants / directions from the node, so we could see the relative size of the blue-agent crowd on each node, etc.

See image below, where base network nodes are white and agents are smaller and with colors.

Additional context
This could very greatly extend the power of mesa in cool ways. :)

[quaquel]

#2430 reimplements the network visualization to now use ax.scatter. It does not by default do this offset for multiple agents, but it would be quite easy to build a custom visualization by using the existing matplotlib network visualization as a template.