:Keep old ColorWheel interface and add extra method to implement

ColorWheel interface.

Author: tobiasmaier

components/pango_opengl/include/pangolin/gl/colour.h

@@ -176,11 +176,17 @@ class ColourWheel : public ColourProvider
     }
 
     /// Return next unique colour from ColourWheel.
-    inline Colour GetNext() override
+    inline Colour GetUniqueColour()
     {
         return GetColourBin(unique_colours++);
     }
 
+    /// Return next unique colour from ColourWheel for ColorProvider.
+    inline Colour GetNext() override
+    {
+        return GetUniqueColour();
+    }
+
     /// Reset colour wheel counter to initial state
     inline void Reset() override {
       unique_colours = 0;