Record claimed code items, and other misc DB fixes

* Create new table to store redeemed codes
* Check if a player already used a code when using /redeem
* Change Coordinate columns to non-plural form
* Fixed EmailItems unique constraint not being specific enough
* Bumped DB version to 3

sql/migration2.sql

@@ -0,0 +1,37 @@
+/* 
+    It is recommended in the SQLite manual to turn off
+    foreign keys when making schema changes that involve them
+*/
+PRAGMA foreign_keys=OFF;
+BEGIN TRANSACTION;
+-- New table to store code items
+CREATE TABLE RedeemedCodes(
+    PlayerID    INTEGER NOT NULL,
+    Code        TEXT NOT NULL,
+    FOREIGN KEY(PlayerID) REFERENCES Players(PlayerID) ON DELETE CASCADE,
+    UNIQUE (PlayerID, Code)
+);
+-- Change Coordinates in Players table to non-plural form
+ALTER TABLE Players RENAME COLUMN XCoordinates TO XCoordinate;
+ALTER TABLE Players RENAME COLUMN YCoordinates TO YCoordinate;
+ALTER TABLE Players RENAME COLUMN ZCoordinates TO ZCoordinate;
+-- Fix email attachments not being unique enough
+CREATE TABLE Temp (
+    PlayerID    INTEGER NOT NULL,
+    MsgIndex    INTEGER NOT NULL,
+    Slot        INTEGER NOT NULL,
+    ID          INTEGER NOT NULL,
+    Type        INTEGER NOT NULL,
+    Opt         INTEGER NOT NULL,
+    TimeLimit   INTEGER NOT NULL,
+    FOREIGN KEY(PlayerID) REFERENCES Players(PlayerID) ON DELETE CASCADE,
+    UNIQUE (PlayerID, MsgIndex, Slot)
+);
+INSERT INTO Temp SELECT * FROM EmailItems;
+DROP TABLE EmailItems;
+ALTER TABLE Temp RENAME TO EmailItems;
+-- Update DB Version
+UPDATE Meta SET Value = 3 WHERE Key = 'DatabaseVersion';
+UPDATE Meta SET Value = strftime('%s', 'now') WHERE Key = 'LastMigration';
+COMMIT;
+PRAGMA foreign_keys=ON;