* glom/print_layout/canvas_layout_item.[h|cc]: Remove the constructor and
create() that take a LayoutItem, because we should put the CanvasItem in a
canvas (even indirectly) before creating the child item, to avoid this
goocanvas bug: https://bugzilla.gnome.org/show_bug.cgi?id=657592#c16
* glom/mode_design/print_layouts/window_print_layout_edit.[h|cc]:
* glom/print_layout/canvas_print_layout.[h|cc]:
Add and use create_canvas_layout_item_and_add() methods which put the new
canvas item in the canvas before creating its child items based on the
LayoutItem.

This fixes bug #668901 (alien)