ui, logic: design for license ui and forcing the user to enter a key on first open

This change integrates the license key ui into the application and makes it necessary for the user to enter a correct
key. The check for a correct key is done on startup and whenever a project is loaded. The check for the key also
includes a check whether the location of the application has changed.

src/lib/Application.h

@@ -35,6 +35,7 @@ public:
 	void loadProject(const FilePath& projectSettingsFilePath, bool forceRefresh);
 	void refreshProject();
 	void saveProject(const FilePath& projectSettingsFilePath);
+	void showLicenseScreen();
 
 	static void setAppSettingsPath(const std::string& appSettingsPath);