background on topic-list, more width on extra-info-wrapper, meta viewport fix

* background on topic-list (matches primary background) so category background images don't render topic pages unreadable
* added more width to the extra-info-wrapper so there's less title white space on the right
* changed meta viewport to solve issue discussed here https://meta.discourse.org/t/zooming-and-initial-display-with-portrait-orientation-on-ipad/16814