FFT size as <select>

[fagci]

Will be handy to set FFT size using <select> control woth predefined values.

Details: often using smaller values to see small BW signals on zoomed out waterfall, but if need to view precise zoomed in signal, will select something between 16k/32k.

[jketterl]

Please use the issue template.

I do understand the idea, but I don't have enough data to make this become reality.

Questions that need to be answered:

What range would the select need to cover?
Does anybody use values that are not powers of 2? Is that even possible?

[fagci]

Range which works for me is: 2^9 .. 2^15 bins.
Above 2^15 not works (waterfall is not visible).
2^9 shows broadcast stations at 40m. Lower is unusable I think =)