Store Themes as JSON files (#4471)

Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/singletons/Theme.hpp

@@ -120,7 +120,9 @@ public:
 
 private:
     bool isLight_ = false;
-    void actuallyUpdate(double multiplier);
+
+    void parse();
+    void parseFrom(const QJsonObject &root);
 
     pajlada::Signals::NoArgSignal repaintVisibleChatWidgets_;