Initial window position without content fix for #279

If window has Content everything is same except "} else if (locationSet && !shown)" where !shown is removed because it didn't make sense because it was always true but actually false(see code at start of method)

Atm InitialLocationManualWithoutContentAndSize is failing for WPF because there is some bug in WPFBackend.Move method compering to WPFBackend.Bounds(called when Size is set)
I think it's somehow connected to Xwt.WPFBackend.WpfWindow.initialX not being set by Move method.

All 3 methods are failing for GTK because known bug of 8px offset.