The default navigation method should be TabbedNavigation

TabbedNavigation is when we have a MainWindow, i.e. the typical use case;
whereas NoNavigation is when using Konsole Part. The code in Part calls
setNavigationMethod(NoNavigation), so things should work as before.

I made a wrong assumption that TabbedNavigation was already the default.

CCBUG: 432077
(cherry picked from commit e693f2d7)