Improves accessibility of the topbar using screen readers

What does this MR do?

Adds a few additional labels to improve the usability of the topbar when using a screen reader to access the page.

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

Very

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings