(Tasklist): Make tasklists global.

data/migration/v0-v1/migration.sql

@@ -0,0 +1,8 @@
+ALTER TABLE tasklist DROP COLUMN guildid;
+CREATE INDEX tasklist_users ON tasklist (userid);
+
+ALTER TABLE tasklist_reward_history DROP COLUMN guildid;
+CREATE INDEX tasklist_reward_history_users ON tasklist_reward_history (userid, reward_time);
+
+
+INSERT INTO VersionHistory (version, author) VALUES (1, 'Migration v0-v1');