mailbox follow-up

Part of #1668

What does this MR do?

• fix toggle read or unread state
• removed edit mode
• show additionaly mail address and name from sender
• fix subject and body in answer mode
• Fixes the download of old attachments: attachments from emails that were sent before are marked by the backend and can be distinguished in the frontend. For this, the dlattach function in MailboxControl needs to be restored.
• Safety fallback for emails with broken sender addresses: the backend will return an empty string as the email address. The frontend shows a placeholder ("Unbekannter Absender") and disables the reply button.
• Use a different field in the table of the inbox (first picture is "inbox", second picture is "sent"):

How confident are you it won't break things if deployed?

Links to related issues

How to test

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text in the release notes to /release-notes/YYYY-MM.md
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.