Extend Return Policy length to 500, reduce app_config key length to 50 (#879)

database/database.sql

@@ -4,8 +4,8 @@
 --
 
 CREATE TABLE `ospos_app_config` (
-  `key` varchar(255) NOT NULL,
-  `value` varchar(255) NOT NULL,
+  `key` varchar(50) NOT NULL,
+  `value` varchar(500) NOT NULL,
   PRIMARY KEY (`key`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;