A new Spectrum analyzer module

Made a spectrum analyzer module. It is FFT based and it uses 8192 points with a Blackman Nuttal window applied over it.

The screen update rate depends on the selected sample rate (5.4 updates/s @ 44k1, 11.6 updates/s @ 96k.

Vertical scale is 12dB/Division, horizontal scale as is indicated by the labels below it.