GST-Tensordecoder-ov_ep/gst/smoothwave

This is a home-grown visualization, with a couple lines of code copied
from synaesthesia.  It draws the waveform in the bitmap, then fades out
the entire bitmap so older waveforms disappear.  It looks OK, but it's
grayscale so far (haven't solved the cmap problems, note all the commented
out code).  I'm going to try to make a much better version as time goes
on.