User settings

This is a pull request for issues #455 and #456.

@mitar, this worked before, but I updated it to match your example.

However, if this error is thrown in a server method, ```field``` won't be sent through the wire. According to [Meteor docs](http://docs.meteor.com/#meteor_error), error is sanitized before sending so that only original ```Meteor.Error``` fields are sent to the client.

So, this error can be used for client side validation only.