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.cpp

@@ -111,6 +111,11 @@ void Application::saveProject(const FilePath& projectSettingsFilePath)
 	}
 }
 
+void Application::showLicenseScreen()
+{
+	m_mainView->showLicenseScreen();
+}
+
 void Application::setAppSettingsPath(const std::string& appSettingsPath)
 {
 	m_appSettingsPath = appSettingsPath;