refactoring: bills service.

refactoring: bills payments made service.

server/src/database/migrations/20200719152005_create_bills_table.js

@@ -14,6 +14,7 @@ exports.up = function(knex) {
     table.decimal('payment_amount', 13, 3).defaultTo(0);
 
     table.string('inv_lot_number').index();
+    table.integer('user_id').unsigned();
     table.timestamps();
   });
 };