Follow the path of a specific subscriber

[carlsverre]

Add a feature which allows the viewer to follow the path of a single subscriber on the notification map page. Either pick a subscriber at random or allow one to be selected. When selected, the map should render the subscribers path over time as well as all of the notifications they have received. By focusing on a single subscriber it would be easier to explain how notifications are being sent out in real time. It also showcases the power of SingleStore to run queries over small fragments of data as well as the entire holistic view.