Add a new profile field for self description

Closes #656 (closed)

What does this MR do?

This MR adds a new field in the profile with a self description visible for the community. The description of the public self description is made clearer.

based on : !1128 (merged)

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