template.slim, claytext.css: don't put block elements in spans

.header, .footer, and .emailquote belong in paragraphs that are
pre-line wrapped, not in spans.
regenerate *.html
mobile.css: don't shrink the font-size of .codeblock further
template.slim: claytext.css before mobile.css

Also regenerate *.html.
mobile.css: make pre.codeblock overflow-y
template.slim, *.css: make .emailquote a pre

We want to do this because `white-space: pre` and overflow-y on
mobiles is a perfect fit.
regenerate *.html