Load resources securely when available

When loading font resources insecurely, browsers report that the site
loads resources over insecure connections.

Especially in "/themes/*/layouts/post.html" and "home.html", when
loading "http://fonts.googleapis.com/css?family=Open+Sans", this element
should be loaded securely so that browsers can safely report that all
elements on an SSL/TLS page are being loaded from secure sources.

Additionally, I searched through the rest of the code and changed
external links to HTTPS when the corresponding sites supported SSL.