[core, file, l10n, page] One commit to rule them all

* Add the video the index page.
* Update some packages, the gulpfile, and the file index.
* Complete all l10ns, including translations, fonts, and sizing.
* Significantly improve carousels, text breaking, and layout.
* Strip trailing slashes when redirecting in nginx.
* Update the terms and privacy policies.
* Fix hreflang tagging once and for all.
* Fix, update, and improve everything else ever.