[hdf5scan] projections, scans and flat field returns now dicts with index as keys and url as value instead of lists

- add `Frame` and frames to filter projections, darks, flats and return projections
- start updating a few properties

- insure that no keys are overwrite when returns the refs_urls
- close partially the nxtomomill issue nxtomomill#1

Manage several ref and serie of ref