Improve Post Scope UI

This adds tooltips on the scope icons which explain the options, the notice box when selecting followers-only visibility on a non-locked/protected account, and the info box when selecting direct visibility.

I mirrored the text from the Mastodon frontend and localizations (I added only English and German, not sure enough about the sentence structure for others). There probably should be a warning/info link in the notice about direct visibility regarding the privacy levels of DMs, but that probably warrants a separate PR? Stock Mastodon links to their ToS in the current version, which feels a little weird.