Overhauls discord verification system (#53289)

This completely replaces the previous verification system, for one that
will interoperate with a discord redbot instance that uses the cogs
located at you github.com/optimumtact/orangescogs

This cuts out several steps in the system, but it also leaves alone the
existing notify system (which just uses a file list of discord ids) as a
record of who to notify

SQL changes required for the new database system

Version 5.10, 7 August 2020, by oranges

Changes how the discord verification process works.
Adds the discord_links table, and migrates discord id entries from
player table to the discord links table in a once off operation and then
removes the discord id on the player table

The user connects to any tg server, and uses the "Verify Discord
Account" verb, this generates a six word one time use token, with a 4
hour time validity period (defined as 4 hours from the timestamp value)
in the discord links table.

This one time token, and the ckey of the user are stored in
discord_links

At this point the entire DM side is done, this is all it does

SQL/tgstation_schema_prefixed.sql

@@ -322,7 +322,6 @@ CREATE TABLE `SS13_player` (
   `lastadminrank` varchar(32) NOT NULL DEFAULT 'Player',
   `accountjoindate` DATE DEFAULT NULL,
   `flags` smallint(5) unsigned DEFAULT '0' NOT NULL,
-  `discord_id` BIGINT(20) NULL DEFAULT NULL,
   PRIMARY KEY (`ckey`),
   KEY `idx_player_cid_ckey` (`computerid`,`ckey`),
   KEY `idx_player_ip_ckey` (`ip`,`ckey`)
@@ -574,6 +573,20 @@ END
 $$
 DELIMITER ;
 
+--
+-- Table structure for table `discord_links`
+--
+DROP TABLE IF EXISTS `SS13_discord_links`;
+CREATE TABLE `SS13_discord_links` (
+	`id` int(11) NOT NULL AUTO_INCREMENT,
+	`ckey` VARCHAR(32) NOT NULL,
+	`discord_id` BIGINT(20) DEFAULT NULL,
+	`timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
+	`one_time_token` VARCHAR(100) NOT NULL,
+	`valid` BOOLEAN NOT NULL DEFAULT FALSE,
+	PRIMARY KEY (`id`)
+) ENGINE=InnoDB;
+
 /*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
 /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
 /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;