CC-430: Audio normalization (Replaygain Support)

-change default database value to null

airtime_mvc/build/sql/schema.sql

@@ -124,7 +124,7 @@ CREATE TABLE "cc_files"
 	"soundcloud_error_msg" VARCHAR(512),
 	"soundcloud_link_to_file" VARCHAR(4096),
 	"soundcloud_upload_time" TIMESTAMP(6),
-	"replay_gain" VARCHAR(16) default '0',
+	"replay_gain" VARCHAR(16),
 	PRIMARY KEY ("id"),
 	CONSTRAINT "cc_files_gunid_idx" UNIQUE ("gunid")
 );