Coloured clips basics

These basics add a colour index to each clip and track, and allow for a choice of four colours to be set from the track menu drop down.  The additional wave colours (red, green and black) are not currently configurable, and the colour index is not currently saved.

src/WaveTrack.h

@@ -161,6 +161,10 @@ class AUDACITY_DLL_API WaveTrack final : public PlayableTrack {
 #ifdef EXPERIMENTAL_OUTPUT_DISPLAY
    void SetVirtualState(bool state, bool half=false);
 #endif
+
+   int GetWaveColorIndex() const { return mWaveColorIndex; };
+   void SetWaveColorIndex(int colorIndex);
+
    sampleFormat GetSampleFormat() const { return mFormat; }
    void ConvertToSampleFormat(sampleFormat format);
 
@@ -606,6 +610,7 @@ class AUDACITY_DLL_API WaveTrack final : public PlayableTrack {
    int           mRate;
    float         mGain;
    float         mPan;
+   int           mWaveColorIndex;
 
 
    //