Replaced austria denns logo on footer page

Closes no issue

What does this MR do?

On request, the Denns logo of foodsharing Austria was exchanged via the support ticket https://foodsharing.freshdesk.com/a/tickets/341 of foodsharing Vienna.

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Links to related issues

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1. Checkout branch locally
2. Login as foodsaver
3. ...

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Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
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