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_gui/qt/view/QtMainView.h

@@ -37,11 +37,13 @@ public:
 	virtual void setTitle(const std::string& title);
 	virtual void activateWindow();
 	virtual void updateRecentProjectMenu();
+	virtual void showLicenseScreen();
 
 private:
 	void doSetTitle(const std::string& title);
 	void doActivateWindow();
 	void doUpdateRecentProjectMenu();
+	void doShowLicenseScreen();
 
 	std::shared_ptr<QtMainWindow> m_window;
 	std::vector<View*> m_views;
@@ -49,6 +51,7 @@ private:
 	QtThreadedFunctor<const std::string&> m_setTitleFunctor;
 	QtThreadedFunctor<> m_activateWindowFunctor;
 	QtThreadedFunctor<> m_updateRecentProjectMenuFunctor;
+	QtThreadedFunctor<> m_showLicenseScreenFunctor;
 };
 
 #endif // QT_MAIN_VIEW_H