Add "listen" to fm functions

[TTVMagicigel1]

doesnt have to be implemented, but id think when broadcasting radio it would be useful if a friend could then listen to that broadcast with his bruce device. also it could be used to listen to ordinary radio ofc. speaker quality isnt a problem on devices like t-embed or t-embed cc1101 either, my solution is to get an extra aux cable and resistor to solder it to the speaker pins. worked fine for me and i then had mono audio on my flip 3. but i think the normal speakers would also be good enough to listen to radio. also you could implement the same feature for rf to listen to walkie talkie frequencies (often at about 446mhz for short range)
thanks for reading this (if you did until here), and as i sai it doesnt have to be implemented, but it can prove useful