diff layer/SpectrumLayer.cpp @ 1212:a1ee3108d1d3 3.0-integration

Make the colour 3d plot renderer able to support more than one level of peak cache; introduce a second "peak" cache for the spectrogram layer that actually has a 1-1 column relationship with the underlying FFT model, and use it in addition to the existing peak cache if memory is plentiful. Makes spectrograms appear much faster in many common situations.