Partial updates to production

This is a set of cherry-picked commits from the `master` branch, to update `production` with a few changes to the tree-viewer:

- Simplified **About navigation** (main menu and sidebar nav), to hide empty/unused pages
- Streamlined and re-organized **Developer Resources** page
- Cosmetic and functional improvements to the **Contact** page

I've tested this branch locally, and I believe it will have no unwanted side effects on the production site. All linked resources in the Developer Resources page are in other domains and should be available already.

(It turns out cherry-picking works very well for this, provided the earlier commits are fairly targeted. Please let me know if I should bring any other changes into this pull request. The Credits page, perhaps?)