Re-enable rocrate dependency

Summary

See: #181 (closed)

Test Environment

• I exported a file from kadi4mat (e.g. https://demo-kadi4mat.iam.kit.edu/).
• I created a venv and installed the pypi rocrate package.
• I verified that the file can be loaded using rocrate. In order to do that unzip the eln file, e.g.: unzip file.eln
• Run the following code using the venv:

  from rocrate.rocrate import ROCrate
  rc = ROCrate("file/")

If it was still broken we would get the following error:

ValueError: no @id in {'@type': 'TextObject', 'encodingFormat': 'text/plain', 'text': 'JSON export of file.'}

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