Button, navbar, and footer

Beta signup button now has an id and extra padding-bottom so it looks
better on phones.

Footer now includes links to all the pages including plan.html which
isn't featured in the navbar.

Created the ashdoc object to house functions that writes html common to
multiple pages so to simply making changes in html.
Created ashdoc.writenavbar and ashdoc.writefooter which does exactly
what as it sounds.  All HTML pages now call these functions.