Better Highlights (#1320)

* Support for user-defined sounds and colors

* Make color & sound columns selectable

* Add custom row for subscription highlights

* Add subscriptions to custom highlights and centrally manage highlight colors

* Dynamically update message highlight colors

src/widgets/helper/ScrollbarHighlight.hpp

@@ -6,17 +6,25 @@ class ScrollbarHighlight
 {
 public:
     enum Style : char { None, Default, Line };
-    enum Color : char { Highlight, Subscription };
 
+    /**
+     * @brief Constructs an invalid ScrollbarHighlight.
+     *
+     * A highlight constructed this way will not show on the scrollbar.
+     * For these, use the static ScrollbarHighlight::newSubscription and
+     * ScrollbarHighlight::newHighlight methods.
+     */
     ScrollbarHighlight();
-    ScrollbarHighlight(Color color, Style style = Default);
 
-    Color getColor() const;
+    ScrollbarHighlight(const std::shared_ptr<QColor> color,
+                       Style style = Default);
+
+    QColor getColor() const;
     Style getStyle() const;
     bool isNull() const;
 
 private:
-    Color color_;
+    std::shared_ptr<QColor> color_;
     Style style_;
 };