Take account of beacons' proximity

[lgnap]

In the settings we can see the power and the approximated distance to the Beacon. If two beacons are detected it will be great to send only a message for the higher power or (better) send the signal power into message ;-)

[ostrya]

I think I would prefer the second option and send the signal power as part of the message. This will probably be done as part of #30 as a new placeholder for templated messages.