Modification to have sponsor pages on plone.org

[erral]

Fixes: #241

Added features:

• Add volto.blocks support to Foundation Sponsors
• Enhance the schema of the Foundation Sponsor Listing to be able to select whether we want to link to each sponsor's page or to their website.

[stevepiercy]

TBH, most of this is way over my head, but I trust you know what you're doing. Nonetheless, it might be a good idea to get someone who has better understanding of the changes to review this before merging.

Or YOLO! and push to testing and see what that looks before deploying to production.

[erral]

Well the YOLO mode doesn't work here, I need at least a seconder to approve the PRs! 👯

[erral]

I will merge this when I receive some input from sponsors to prepare some pages in testing first, before pushing to prod.