Prevented users from signing up with an email/username which was already present in the migration database.

src/server.js

@@ -195,6 +195,9 @@ async function asyncKickStart(){
     //Run legacy migration
     await migrationModel.ingestLegacyDump();
 
+    //Build migration cache
+    await migrationModel.buildMigrationCache();
+
     //Calculate Toke Map
     await tokeModel.calculateTokeMap();