unique: true works bad with sails-mongo.

[misterjt]

I happened to notice on my production server that i can create several users with the same username or emails. I use mongodb on this server.
I started to google, and found, that sails-mongo almost not working with unique:true.
Сould you please implement an additional check on the uniqueness of username and email?

[tjwebb]

You can extend the models to add whichever constraints you wish. If you'd like to add this to the core, please submit a PR