Converted MySQL migration history to the new format

Replaced all NNN_StoreName.sql migration resources with a more
readable, single-file-per-store

OpenSim/Data/MySQL/Resources/Avatar.migrations

@@ -0,0 +1,12 @@
+:VERSION 1
+
+BEGIN;
+
+CREATE TABLE Avatars (
+	PrincipalID CHAR(36) NOT NULL, 
+	Name VARCHAR(32) NOT NULL, 
+	Value VARCHAR(255) NOT NULL DEFAULT '', 
+	PRIMARY KEY(PrincipalID, Name), 
+	KEY(PrincipalID));
+
+COMMIT;