This example demonstrates how to display currently ongoing transmissions,
ongoing receptions, and radio signals as they propagate through the medium.

The adhoc wireless network contains 3 nodes, a source, an intermediate node, and
a destination. The source node continuously pings the destination node through
the intermediate node.

When you run the example, the medium visualizer displays an animated gif at the
nodes which are currently transmitting or receiving a signal. Moreover, it also
shows the signals as semi-transparent rings growing over time as they propagate
through the medium.
