general: Make most settings a BasicSetting

Creates a new BasicSettings class in common/settings, and forces setting
a default and label for each setting that uses it in common/settings.
Moves defaults and labels from both frontends into common settings.
Creates a helper function in each frontend to facillitate reading the
settings now with the new default and label properties.

Settings::Setting is also now a subclass of Settings::BasicSetting. Also
adds documentation for both Setting and BasicSetting.

src/yuzu_cmd/config.h

@@ -8,6 +8,8 @@
 #include <memory>
 #include <string>
 
+#include "common/settings.h"
+
 class INIReader;
 
 class Config {
@@ -22,4 +24,8 @@ public:
     ~Config();
 
     void Reload();
+
+private:
+    template <typename Type>
+    void ReadSetting(const std::string& group, Settings::BasicSetting<Type> setting);
 };