Add support for embedding Pixelfed posts

[stefanbohacek]

Pixelfed uses iframes for embedding posts, and also supports Mastodon's /api/v1/statuses/ endpoint, but it currently requires authentication.

This requirement should be removed in the future, so once that's in place, work on this can resume.

[stefanbohacek]

Thanks to @ThisIsMissEm's work in pixelfed/pixelfed@1eadff9, the work on this can resume.

[ThisIsMissEm]

Was this a CORS issue? It reads like an oauth issue?

[stefanbohacek]

@ThisIsMissEm Oh, I think you're right, this is a separate issue, sorry!

Still, great work!