Extract table from gene list

Allow to download .csv of metadata for a filtered list of genes.

Limited to 100000 for the moment, like the fasta files

Closes #126

backend/metagenedb/api/catalog/qparams_validators/gene.py

@@ -15,3 +15,4 @@ class GeneQueryParams(PaginatedQueryParams):
     function = fields.String()
     source = fields.String()
     fasta = fields.Boolean()
+    csv = fields.Boolean()