logic: Application settings migration system

* Added version number to ApplicationSettings
* Added SettingsMigrator for defining migration rules for different ApplicationSettings versions
* Migrate ApplicationSettings when loading

src/lib/settings/ApplicationSettings.h

@@ -10,9 +10,14 @@ class ApplicationSettings
 {
 public:
 	static std::shared_ptr<ApplicationSettings> getInstance();
+
+	static const size_t VERSION;
+
 	ApplicationSettings();
 	~ApplicationSettings();
 
+	bool load(const FilePath& filePath);
+
 	bool operator==(const ApplicationSettings& other) const;
 
 	int getMaxRecentProjectsCount() const;