Add teaching resources to clusters

Link to other resources beyond the reading list

Add buttons below sub-cluster description which open up these resources above the readings.

For each view, highlight top resources per cluster - top 5, then show more. Do rough pass now, then ask specialists to correct

Explain "specialist resources" on hover

Data sources:

- Lesson plans & slides: https://forrt.org/lesson-plans/ plus new list from @max-fw
- Syllabi: from website https://forrt.org/syllabus/
- Games: https://docs.google.com/spreadsheets/d/1cmydWjD1OuyKxJVfDlv0N3T474zwymfB04yFDZQO-TY/edit?gid=610093275#gid=610093275

Deduplicated across sources:
- Reading is only in the clusters
- Any syllabus is only in syllabi
- Lesson plans there
- And only the remainder in curated resources

Make sure sub-clusters without resources are not shown (@flavioazevedo, I removed "study design" that had only a repeated study)