Unify updating navigation actions

On the Quick side, navigation actions were dependent on the context menu.
They were only updated when requesting a new context menu and this is
obviously wrong if an action is tied to a button or another type of UI
element.

Change-Id: I5f14b019b66215f16d027fb57d76f052b1604365
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>