Updates

- Filter-related updates (this is most of this pr).
- Adds a `.u-align-with-btn()` utility mixin.
- Refactors some utility mixin names to be more consistent. Some were using the `u-` prefix and some were not. Also rolled media query mixins into the utilities docs.
- Updates the layout, turns out the narrow main content area is only for long reading text pages like the post page.
- Makes index page static again.
- Updates to latest version of cf-expandables.