configuration: setup global configuration checkbox

Global config checkbox now enables/disables the appropriate tabs in the game
properties dialog. The use global configuration setting is now saved to the
config, defaulting to true. This also addresses some changes requested in the PR.

src/core/settings.h

@@ -382,7 +382,7 @@ enum class GPUAccuracy : u32 {
     Extreme = 2,
 };
 
-typedef struct Values_t {
+struct Values {
     // System
     bool use_docked_mode;
     std::optional<u32> rng_seed;
@@ -489,7 +489,10 @@ typedef struct Values_t {
 
     // Add-Ons
     std::map<u64, std::vector<std::string>> disabled_addons;
-} Values;
+
+    // Per-Game Settings
+    bool use_global_values;
+};
 
 extern Values global_values;
 extern Values game_values;