Display summary of attachments in description, and mark up content
warning if present, e.g.:

    Attached: 3 images · Content warning: Dota 2

When text is not supposed to be hidden, it looks more like:

    Attached: 3 images

    Here is the text of the toot

With #6817, multilinguagility should be assured...

* Save metadata from video attachments, put correct dimensions into OG tags

* Add twitter:player for videos

* Fix code style and test

Reasoning: HTML title tag affects everyone. But OpenGraph only affects
when somebody is deliberately sharing the content, usually in an
environment where such content is expected. Hiding the content in
OpenGraph tags results in deceitful previews which inhibit the
shareability of the post.

Example: Somebody writes a clever post about politics but kindly
puts a "uspol" content warning on it. Mastodon users are thankful,
but sharing this post on another platform results in non-Mastodon
users believing the entire contents of the post is "uspol" and not
clicking through/reading and re-sharing.

- Return all images as og:image
- Return videos as og:image (preview) and og:video
- Return profile:username on profiles