Fix things mentioned during code review

Ref: https://github.com/dolphin-emu/dolphin/pull/4917

Source/Core/Common/Config/Config.h

@@ -0,0 +1,63 @@
+// Copyright 2016 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <functional>
+#include <map>
+#include <memory>
+#include <string>
+
+#include "Common/Config/Enums.h"
+#include "Common/Config/Layer.h"
+#include "Common/Config/Section.h"
+
+namespace Config
+{
+using Layers = std::map<LayerType, std::unique_ptr<Layer>>;
+using ConfigChangedCallback = std::function<void()>;
+
+// Common function used for getting configuration
+Section* GetOrCreateSection(System system, const std::string& section_name);
+
+// Layer management
+Layers* GetLayers();
+void AddLayer(std::unique_ptr<Layer> layer);
+void AddLayer(std::unique_ptr<ConfigLayerLoader> loader);
+void AddLoadLayer(std::unique_ptr<Layer> layer);
+void AddLoadLayer(std::unique_ptr<ConfigLayerLoader> loader);
+Layer* GetLayer(LayerType layer);
+void RemoveLayer(LayerType layer);
+bool LayerExists(LayerType layer);
+
+void AddConfigChangedCallback(ConfigChangedCallback func);
+void InvokeConfigChangedCallbacks();
+
+// Explicit load and save of layers
+void Load();
+void Save();
+
+// Often used functions for getting or setting configuration on the base layer for the main system
+template <typename T>
+T Get(const std::string& section_name, const std::string& key, const T& default_value)
+{
+  auto base_layer = GetLayer(Config::LayerType::Base);
+  return base_layer->GetOrCreateSection(Config::System::Main, section_name)
+      ->Get(key, default_value);
+}
+
+template <typename T>
+void Set(const std::string& section_name, const std::string& key, const T& value)
+{
+  auto base_layer = GetLayer(Config::LayerType::Base);
+  base_layer->GetOrCreateSection(Config::System::Main, section_name)->Set(key, value);
+}
+
+void Init();
+void Shutdown();
+
+const std::string& GetSystemName(System system);
+System GetSystemFromName(const std::string& system);
+const std::string& GetLayerName(LayerType layer);
+}