Replace custom insertion_model by serializers

Also added few tests for insertion of Genes to DB in the import_from_igc.py script.

Maybe we could externalize the functions used to make them reusable by other scripts.

Closes #28

backend/dev_data/IGC_sample.annotation_OF.summary

@@ -999,3 +999,4 @@
 999	158499257-stool1_revised_C1458534_1_gene127873	11955	Complete	USA	unknown	unknown	unknown	NOG295308	0.00315706393054459	0.00280373831775701	unknown	unknown	USA
 1000	MH0385_GL0059251	11946	Lack both ends	EUR	unknown	unknown	unknown	unknown	0.000789265982636148	0.000934579439252336	unknown	unknown	EUR
 1000	MH0385_GL0059251	11946	Lack both ends	EUR	unknown	unknown	unknown	unknown	0.000789265982636148	0.000934579439252336	unknown	unknown	EUR
+353535	wrong_length	the_length	Info	EUR	unknown	unknown	unknown	unknown	0.0000001	0.00000001	0.0000001	unknown	unknown	EUR