feat(skipLink): Add skip link to Pajamas site

Current behavior

• Focus starts at the top of the navigation and traverses through all of it before getting into the page content.

New behavior

• Focus starts with the skip link, which is visible when it receives focus.
• Activating the skip link places focus on the h1.
• Tabbing traverses through the page content.

Before	After

Closes #1153 (closed)