Use polling approach to trigger comms to other robots

[fcladera]

This PR changes the approach for triggering communications between robots:

• Before we used watchers (watchstate), which was a passive system that triggered callbacks when the internal state of a robot was modified. This has the disadvantage that robots that are stationary wrt each other may not trigger comms.
• Now we use a polled system that triggers comms regularly.

Fixes #10