logic: Show error message when license expired

* moved all license checking logic to LicenseChecker
* create LicenseChecker instance in app
* Notify MainView with MessageForceEnterLicense

src/lib_gui/qt/window/QtLicense.h

@@ -19,6 +19,8 @@ public:
 	void clear();
 	void load();
 
+	void setErrorMessage(const QString& errorMessage);
+
 protected:
 	// QtWindow implementation
 	virtual void populateWindow(QWidget* widget) override;