Retrofit the nag bar for themes with fixed headers

This was written specifically for the fixed header in the Twenty-Fourteen theme, but with some basic changes this solution can be made to suit most themes with fixed headers.

Changes to css/liveblog.css are principally to set default states for the Twenty-Fourteen theme including the various media query conditionals.

Changes to js/liveblog.js are to check for a fixed header or the administrator's bar, and offset the nag bar accordingly. It is assumed that the theme's fixed header is positioned with the admin bar taken into consideration as is the case with Twenty-Fourteen.