Resolve "Add possibility of querying annotations of datafiles"

Closes #118 (closed)

ajoute recherche "key-value pairs"

secure/datafiles/list/json/lookup/str:key/str:value/

secure/datafiles/list/json/lookup/str:key/str:value/str:DatasetID/

Recherche est exact (recherche exacte de la clé avec la valeur)