set text description for bibliography objects

Former-commit-id: 597653983920124084343ec32ccc26a13cef7067

ippisite/ippidb/models.py

@@ -40,6 +40,8 @@ class Bibliography(models.Model):
     class Meta:
         verbose_name_plural = "bibliographies"
 
+    def __str__(self):
+        return '{}, {}'.format(self.source, self.id_source)
 
 
 class Taxonomy(models.Model):