add server.connect method that accept Mongo URI

These changes is demonstration. According to http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html `mongo-sync` needs API to be able to connect to Mongo servers / clusters using connection string. 

Implemented API proporsal is excessive:
```
var db = new mongo.Server(host, port).connect(MONGO_URI);
      app.db = server.;
```

Please, consider to add this or something related.