Added newsletter signup in sidebar

Added newsletter signup in sidebar, powered by mailchimp.

Also, added media query to set font size on "About the author" in the sidebar,
so that it doesn't wrap.

    application/models/globals.php
    application/views/articles/2013_08_oeis.php
    application/views/sidebars/sb_article.php
    css/style.css
    images/mailchimp.png   (+)