Save custom domain type name

[nechaido]

It would be good to have a name property for custom types defined in ./types.js for a Model.
That I would be able to use proper types in ERD generation

Additional context
metarhia/metagram#2 (comment)

[tshemsedinov]

You may use:

• Model.prototype.types
• Schema.prototype.findType
• Schema.prototype.findReference