message: Add search box structured data
diff: extends ../../../components/layout/layouts/blank
  +block meta
  + script( type="application/ld+json" ).
  + {
  + "@context": "http://schema.org",
  + "@type": "WebSite",
  + "url": "https://www.are.na/",
  + "potentialAction": {
  + "@type": "SearchAction",
  + "target": "https://www.are.na/search/{search_term_string}",
  + "query-input": "required name=search_term_string"
  + }
  + }
  +
  block container
  include ../../../components/logged_out_nav/templates/header
  