Make format_title param work with headline

format_title is a front matter parameter which turns off title case transformation on title and the page title in breadcrumbs.

We should also extend this to headline as the headline is typically used as the page title.

Currently, to not have title case, we can do things like:

headline: <span>openPASS</span>

But it feels like a hack. Extending format_title to headline would make this feel right.