Csv export import

[TimoBroeskamp]

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Closes #8356

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The UI of this prototype is not final and I am open for any recomendations on how to build it more intuitively.

[TimoBroeskamp]

The Unis tests fail because I added another element to the dom that the test checks for changes.

These are images of my prototype:

As you can see there is a "Download CSV" button and a fourth option in the toolbar tu upload users that opens the dropzone.