Minor improvements to the previous PR #395 Add Gain_TX to Replay App

[Brumi-2021]

This PR , is an an update of the previous one #395,
about Replay App , correcting two several minor issues. (inspired with the job of Mic App contributors . Thanks !!!)

Before talking about the MINOR IMPROVEMENTS, let me share the updated previous frontend RF chart.,
where I added more details , showing now :
usual fw code ref. var labels //adj. margin range // adj. steps // and usual LCD GUI labels.

MINOR IMPROVEMENTS :
1-) In previous code , any RX(rf_amp) user setting modification (in any receiver App ) ,
was modifying at the same time the TX (rf_amp) in Replay App and viceversa. (that might be sometimes confusing and annoying ). (That is not happening in the rest of TX App like ex. Mic App) . Then, this has been addressed in this PR

2-) In previous code , while we were in play mode , we could modify “in real time” the TX (rf_amp) (that was good ) , but the TX LED was following that rf_amp toggle setting (that was incorrect) because while we are in play mode, we were always in TX mode. (so TX_LED should be constant in ON while we are transmitting the file ).This has been addressed in this PR, but now , it is ignored any "live changes " of tx-freq, tx-gain . tx-rfamp, till next "stop" and "play" or next automatic "loop" .

3-) This time we also communized the TX rf_amp GUI interface , (0 / 14 dBs gain) , same as Mic App .

Note :
same as before ,
i-) to avoid any RF amplifier IC , 14dB’s, accidental damage (if user has no antenna connection or antenna missmatching ) - , the first “play” will not use max radiation antenna power . The initial values are (GAIN =35 (-12dB's max) , TX(rf_amp) = 1 =+14dB's) , but of course after first “stop”, any other adj. of freq. / GAIN /, rf_amp, …, will be applyied at every new “play” or new “automatic loop” . (so user will be able to put in max , but not the initial "play")

CONFIRMATION
I checked in three RECEIVER App's , (ex. in ADSB- App ,, or Capture App , or Audio receiver ) that now , any RX_AMP setting is independent from the selected TX_AMP in the Replay App. (I did not check all, but i believe that all are now ok).