Element import: lot of improvements

app/Resources/SonataAdminBundle/views/layout.html.twig

...yBundle/Controller/Admin/ImportDynamicAdminController.php

src/Biopen/GeoDirectoryBundle/Document/OptionValue.php

...GeoDirectoryBundle/EventListener/ElementJsonGenerator.php

...dmin/core_custom/custom-fields/mapping-ontology.html.twig

...dmin/core_custom/custom-fields/mapping-taxonomy.html.twig

.../Resources/views/admin/edit/edit_import_dynamic.html.twig

...oDirectoryBundle/Services/ElementImportMappingService.php

...n/GeoDirectoryBundle/Services/ElementImportOneService.php

...open/GeoDirectoryBundle/Services/ElementImportService.php

web/test.json