add compatibility with old frontend version by adding empty groups list when no sub-group exist (only for deprecated API)

Refactoring data src

Remove any remaining data from this project.

Add a secondary data source. A DB containing the scientific data (ADNI, CHUV, ...) should be linked and a DB containing related meta-data (variables hierarchy, types, ...) should be linked too. This meta-data DB is also used to store articles, models, experiments and so on.


See merge request !31