Add child topics list and prev / next links to topic footer based on subject nav

[briandominick]

Use a little jQuery to glean the parent/child/sibling topics and provide links in the topic footer (bottom of the <main> content container in a topic page).

• ↑ Previous: Parent Topic Title (for a first-child topic)
• ← Previous: Sibling Topic Title
• Next: Sibling Topic Title →
• Next: First Child Topic Title ↓ (for parent topics)

Also generate a list of child topics when a topic has kids in the menu and use that in place of related links (or in addition to?).

Make these configurable, of course.