add ui and viewport scale option, fix combobox items height from parent

src/settings.h

@@ -32,4 +32,9 @@ public:
     {
         return I.Descriptor::value<T>(key);
     }
+    template <typename T, typename D = decltype(T::value)>
+    static D value_or(const std::string& key, D def)
+    {
+        return I.Descriptor::value_or<T, D>(key, def);
+    }
 };