Store banned IP addresses as plain text

Inspired by commit 32c8d0c (Store last login address as plain text,
2016-03-13).

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

schema/aur-schema.sql

@@ -376,7 +376,7 @@ CREATE TABLE IF NOT EXISTS TU_Votes (
 -- Malicious user banning
 --
 CREATE TABLE Bans (
-	IPAddress INTEGER UNSIGNED NOT NULL DEFAULT 0,
+	IPAddress VARCHAR(45) NULL DEFAULT NULL,
 	BanTS TIMESTAMP NOT NULL,
 	PRIMARY KEY (IPAddress)
 ) ENGINE = InnoDB;