Propagation display in 1.3.53

Hi Michael,
I saw that you incorporated and fixed the pull request for displaying radio propagation on the map. I tried to figure it out how it works from the code, but it would be easier if you summarize how it supposed to work in a couple of sentences.


press control-w. i will move the config screen once more testing has been done. as ive caught some bugs already, and didn’t want to release knowing it could causing issues.