Avoid using deprecated GtkAlignment
Avoid GtkCellArea critical warnings in thumb view

GTK+ switched from using constructor() to constructed() in GtkIconView,
which exposed that Cheese does not chain up in the CheeseThumbView (a
GtkIconView subclass) constructed() vfunc. Chain up at the start of
constructed() so that the construct-only properties of the GtkIconView
are set before calling icon view API.