reworking where templates are

Need me some code review on this.

This commit basically just moves the default templates into templates/default, and it removes some logic about specifying a custom path in config for those templates. So that's a small limitation of this, but at least now there's an obvious place to put custom templates.

Also a favicon has been added to the default template, if you set your favicon image to /static/images/favicon.png.

One of the interesting things is that the URLs for stylesheets, scripts, and such will always be the same no matter the theme. So I'm not sure if that's something that we'd want to change. But /static/style.css would be completely different if an admin changed the site's templates. If a user had a cached stylesheet that referred to some different HTML or something, that could get weird.