Make OpenGraph and Twitter meta settable on pages
They're largely hard-coded in ac45cf87. Everything in there should be settable on the page if it's not site-specific:
-
og:image
+twitter:image
plusog:image:type
,og:image:width
, andog:image:height
-
og:description
+twitter:description
-
og:title
andtwitter:title
already come from the page title?