Imprint and privacy

[ChristophNiehoff]

Added possibility to add imprint and privacy notice links.

[ChristophNiehoff]

@ghost91-
You asked why the line
Board.prototype.componentDidMount = jest.fn();
was needed.

It appears that the Board component performs some REST calls in its componentDidMount hook. This is probably not optimal. As a quickfix I changed it to
Board.prototype.apiGetRequest = jest.fn();

Without this mock, the tests fail in the Github Action. (But not on my local machine....)