Hide metadata if they are 'unknown'
Hide the metadata displayed if they are 'unknown'. However, some metadata are still displaying 'unknown' for it is the proof of not knowing, rather than just a missing metadata in the pipeline. These metadata could be found in the future and then correctly displayed when corrected, for instance the repository institution or the specie linked to a Paleontology dataset. Solves #26 (closed).
Edited by Guillaume Gaisne