re-structure menu, darken UI

Source/PresetBank.h

@@ -10,6 +10,12 @@ struct Patch
     float v[prm::num];
 };
 
+struct CategoryIndex
+{
+    juce::StringArray names;
+    std::vector<std::vector<int>> patchIndices;   // parallel to names
+};
+
 class PresetBank
 {
 public:
@@ -21,6 +27,10 @@ public:
 
     void writeTo (int i, juce::AudioProcessorValueTreeState&) const;
 
+    const CategoryIndex& categories() const { return catIndex; }
+
 private:
     std::vector<Patch> patches;
+    CategoryIndex catIndex;
+    void buildCategoryIndex();
 };