range banding revisited

Tentative and temporary ranging solution intended to soon be swapped out with a robust library.
What you could do instead could be:
whenever you're notified at the list of nearby beacons has changed:
- if there's no beacon, wait for 1 sec before updating the UI.
- if there are already some beacons, wait for 5 sec before updating the UI.

It means that you'll have to trigger a timer (that will run only once) when you're notified of a change.
And make sure that you're triggering only one timer.