Provide page titles, align titles, pluralize

This makes us more consistent about having a Registries (plural)
page, with a matching title, with each registry being more consistent
about its linking and name.

This does not make everything perfectly consistent due to lack of
time to track down all of the magical places where Jekyll or Liquid
does whatever it does.  For example, I cannot find where "Tag Kind"
singular comes from in one list when it is plural everywhere else,
among other minor inconsistencies.