Include Changes for specification V2.0.0

[HLWeil]

This PR merges all changes accumulated for the Version 2.0.0 of the specification into the main branch. Afterwards, Version 2.0.0 will be released.

• Big Overhaul of data representation by @hlweil

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• Mechanisms for ARC Quality Control section by @kMutagene

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• Various changes to xlsx table representation

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• Make study section in investigaiton file optional

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• Various clarifications and fixes

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Input would be very welcome, @kappe-c @floWetzels @ZimmerD @kMutagene @Freymaurer @chgarth @muehlhaus @gdoniparthi

[HLWeil]

@Freymaurer @kappe-c @kMutagene Thanks a lot for your input!

I made some changes according to your comments. Please check again if your remarks are resolved now!