Add navigation elements to pages where pagination occurs

This applies to the top-level list of microcosms, items within microcosms,
and comments on commentable items.
Modify link array -> link map processor

This now processes top-level items (e.g. item.meta.links) as well
as collections, and items within those collections. Modifying the
link array to a map is purely for caller convenience.
Generic view code for single items and lists includes pagination nav