to all other pages
This allows resetting all other pages to use the guide configuration
for the current page. Since guides are now single page only (required
to handle mixed page size/orientation layouts), this is a shortcut
to allow guide configuration to be setup on a single page and then
easily transferred to all other pages in the layout.
The class is a QAbstractListModel subclass, making it easy
for creation of different views showing the guides in a layout.
Additionally, a QSortFilterProxyModel (QgsLayoutGuideProxyModel)
has been created to filter QgsLayoutGuideCollection to guides
with matching page numbers and orientations.
