Improve translating posts via Mastodon api

[connyduck]

This does 4 things:

• Alt text is now translated when opening media of translated posts. Previously only the long-press alt text was translated.
• The translate button is now hidden on non-public posts. The Mastodon api returns 403 there.
• Translated posts will only be collapsible when the original was collapsible as well. It is just weird when an "show more" button suddenly appears because the post got longer by translating it.
• The translation status and the untranslate button are now shown below each other instead of next to each other. Looks way better on smaller display or long texts.

Before / After