As notifications appear in the time+date dropdown's message list, there's
a strong relationship between notification banners and the menu. However
while the time+date menu is centered by default, which matches the banner
position, its actual position depends on the session mode - in particular
it is moved to the right in classic mode.
Reinforce the relationship in these cases by moving notification banners
underneath the time+date menu.
https://bugzilla.gnome.org/show_bug.cgi?id=745910
e4974beebf