[#796] Skittlish Dreams: mobile style

* move column-specific CSS to a media query

* don't move the entry userpic CSS to a media query though; that
  positions the icon in the entry and doesn't affect overall readability
  of the layout

* set a line-height on the navlinks so that they don't overlap when
  they're on multiple lines on small screens

* make the modules at the bottom full-width on smaller screens

* print meta viewport tag

Fixes #796