WaveNet: use another NAM as module processing conditioning input

[sdatkinson]

Currently, the condition input is passed into each Layer of the WaveNet layer arrays via a 1x1 convolution. This feature adds another (multi-channel out) NAM in between.

This will be investigated during A2 development to have a "conditioning WaveNet" compute the features that condition the "main WaveNet."

[sdatkinson]

Changing to just a WaveNet since weight-setting API isn't defined at the DSP level. Can expand later, but I'm not expecting to look into it for A2.

[sdatkinson]

Update: got it to work with general nam::DSP instances :)