Add reference field to offer admin page.

coin/offers/admin.py

@@ -13,7 +13,7 @@ import autocomplete_light
 
 
 class OfferAdmin(admin.ModelAdmin):
-    list_display = ('get_configuration_type_display', 'name', 'billing_period', 'period_fees',
+    list_display = ('get_configuration_type_display', 'name', 'reference', 'billing_period', 'period_fees',
                     'initial_fees')
     list_display_links = ('name',)
     list_filter = ('configuration_type',)