Update pinned child pages on page rename

When a page which holds a PinnedChildPagesClass object gets renamed, the object should be updated to point at the new child pages references after rename. Currently only the case where child pages get renamed is handled, not the one when the parent page gets renamed, eg A.WebHome with subpages A.A1.WebHome,A.A2.WebHome,A.A3.WebHome getting renamed to B.WebHome, whose PinnedChildPages object should point at B.A1.WebHome, B.A2.WebHome, B.A3.WebHome after rename.