#75 refined peak bins display

[Craig Stuart Sapp]

When the spectrogram is being calculated with
the zero-padded signal to interpolate the frequency
values in the DFT (FFT), then it would be nice to
use that extra information in the display of the
"Peak bins" form of the spectrogram.

For example, there are currently 4 sub-bins for
each non-zeropadded FFT bin. The "peak bins"
display will show the entire non-zeropadded
FFT bin. It would be nice if the four sub-bins
were examined, and the loudest sub-bin were
displayed instead.

Optionally, there could be two related display
types:
"peak bins"
"refined peak bins"
to show either the non-zerpadded bin peaks,
or the zero-padded sub-bin peaks.