Move sidenav position on mobile view

[apburnes]

When a user is looking at the site from a mobile or tablet view then the side, sub navigation should collapse and stick to the top to the window to improve the navigation experience.

Acceptance Criteria

• [ ] The side nav keeps its current layout and functionality when using a view larger than a tablet
• [ ] The side nav collapses into an accordion component when the view is tablet or smaller
• [ ] The side nav sticks to the top of the window view while scrolling down the page

Current functionality

• Side nav is pushed beneath the content when the view is tablet or smaller.
• Users' cannot easily navigate the heading anchors on page with sub nav when the view is tablet or smaller.

Security Considerations

none