Add plot bandwidth measurement to UI

[andreiva]

I thought it would be handy to see signal bandwidth in kHz when adjusting plot deviation. See screenshot I used signals and slots to update the UI, for that I had to move Tuner instantiation to MainWindow. I have very little experience with QT, so I'm not sure if I did it right.

[devnulling]

This would be really useful to have, but looks like it's out dated. @andreiva could you rebase it to make it easier for @miek to merge?

[andreiva]

Sure, I will take a look at it.

It occurred to me, that it would be a lot easier to display BW directly in spectrogramplot. It would probably be doable right in spectrogramplot.cpp. For example above bw rectangle? Any opinions? It was somehow ugly how I had to pass bw value to spectrogramcontrols.cpp

[luzpaz]

Is there any chance this will ever be merged ?