[#77] Entities: Add AreaComContract to group area commitments together

Tests/Resources/Sql/BillingDelete.sql

@@ -3,7 +3,7 @@
 DELETE FROM credit;
 DELETE FROM payment_variant;
 DELETE FROM delivery;
-DELETE FROM area_commitment;
+DELETE FROM area_commitment_contract;
 DELETE FROM area_commitment_type;
 DELETE FROM season;
 DELETE FROM wine_attribute;