Fix Global Header and Footer appearance.

- Remove border-radius from Global Header. Since it is full width
  content, all borders should be sharp so it can fit to window.

- Align copyright to left when it is displayed on mobile devices.

- Wrap copyrights with <small> instead of <p>. See below for this.
  http://www.whatwg.org/specs/web-apps/current-work/#the-small-element