Add 'Reduced CPU Usage' menu option and config entry.

src/process/SpectrumVisualProcessor.cpp

@@ -201,6 +201,14 @@ void SpectrumVisualProcessor::setFFTSize(unsigned int fftSize_in) {
     fftSizeChanged.store(true);
 }
 
+unsigned int SpectrumVisualProcessor::getFFTSize() {
+    if (fftSizeChanged.load()) {
+        return newFFTSize;
+    }
+    return fftSize.load();
+}
+
+
 void SpectrumVisualProcessor::setHideDC(bool hideDC) {
     this->hideDC.store(hideDC);
 }

src/process/SpectrumVisualProcessor.h

@@ -47,6 +47,7 @@ public:
     
     void setup(unsigned int fftSize);
     void setFFTSize(unsigned int fftSize);
+    unsigned int getFFTSize();
     void setHideDC(bool hideDC);
     
     void setScaleFactor(float sf);