New demod band parts based on Daniel Sigg's Demod-decimation-band parts

These parts have a hard-coded, phase locked demodulation at fixed frequencies evenly spaced between 0 and the nyquist frequency. They therefore do not have a frequency input. Output is in I&Q pairs, except output 1 is the signal reproduced without demodulation, and output 2 is the demodulation at the nyquist frequency: neither of which has a pair.

All other outputs are demodulated on evenly spaced frequencies from 1/n to n-1/n times the nyquist frequency, for n is the number of bands on the part.

Outputs are all filtered as for 8x decimation 8x, appropriate for converting from 524k models to 65k IPCs, for instance.