Zenodo integration
Adds support for integration with Zenodo data repository using:
- zenodo_dataset_stage_in liquid tag for staging in datasets from Zenodo instance to computations
- zenodo_file_stage_in liquid tag for staging in single files from Zenodo instance to computations
- zenodo_stage_out liquid tag for uploading results of computations to a deposition on the Zenodo instance
Other changes:
- small refactor of external data repository integration concept overall - towards generic solution
- tests for testing insertion of correct curls for uploading and downloading from Zenodo into scripts