Added page title and logo to page template.

[patrickcate]

Work as part of Issue #22.

• Changed order of header id and class attributes to be consistent with the rest of the file.
• Changed name of header content id to better reflect content.
• Fixed incorrect use of the main tag (https://developer.mozilla.org/en-US/docs/Web/HTML/Element/main) which was being used to wrap header content as well as the main content. Replaced with .page div.
• Added logo w/homepage link to page template.
• Added page title w/ prefix and suffix to page template.
• Added 'contentinfo' role to footer tag.
• Added placeholder logo.png

[fureigh]

Thanks for this, @patrickcate! Looking forward to reviewing.