Do not wrap QQuickView with createWindowContainer
This is motivated by the fact that use of createWindowContainer apparently breaks Wayland text input for KTouch (specifically, it causes issuse with keyboard focus, which is "platform dependent" with createWindowContainer). This commit keeps the QWidgets- based menu that createWindowContainer allowed mostly intact, only getting rid of the keyboard shortcuts customization dialog (whose only useful option was probably to make the window fullscreen) and recreating the full screen menu item, as the KActionCollection-based one assumes the window is QWidget-based.