Splits parent bar into parents and siblings
Adds timestamps to items
Refactors 48px thumbnails into partials

Used in the parent/sibling nav bar, and will soon be used in child partials.
Partial takes a required :item local variable for the item to be thumbnailed,
and an optional :highlighted variable for any thumbnail that will be highlighted
(usually "self" or "self.parent") and an optional :no_link variable that
prevents hyperlinking.