Added option to schedule sending

setup/sql/upgrade-00003.sql

@@ -0,0 +1,12 @@
+# Header section
+# Define incrementing schema version number
+SET @schema_version = '3';
+
+# Adds new column 'scheduled' to campaigns table. Indicates when the sending should actually start
+ALTER TABLE `campaigns` ADD COLUMN `scheduled` timestamp NULL DEFAULT NULL AFTER `status`;
+CREATE INDEX schedule_index ON `campaigns` (`scheduled`);
+
+# Footer section
+LOCK TABLES `settings` WRITE;
+INSERT INTO `settings` (`key`, `value`) VALUES('db_schema_version', @schema_version) ON DUPLICATE KEY UPDATE `value`=@schema_version;
+UNLOCK TABLES;