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/component/view/MainView.h

@@ -16,6 +16,7 @@ public:
 	virtual void setTitle(const std::string& title) = 0;
 	virtual void activateWindow() = 0;
 	virtual void updateRecentProjectMenu() = 0;
+	virtual void showLicenseScreen() = 0;
 };
 
 #endif // MAIN_VIEW_H