Implement the bottom page navigation block

Implement the bottom page navigation block - This block should be optional in the backend. The links should be automatically defined this way:

• For parent pages: the links should show other parent pages at the same level (the previous and the next one in the primary navigation menu order)
• For child pages: the links should show the parent page that is tied to the child page

Designs for desktop and mobile are available here (WIP)