Dynamic Label Feature

[rclai]

Sort of like autoValue where you can do this.field('someOtherField'). Example:

{
    type: String,
    label: function () {
         if (this.field('someOtherField').value === 'someValue')) {
                return 'My Custom Label';
         }
         return 'My Default Label';
    }
}

Further, if this field was within an array or deeply embedded in arrays it would be useful to reference

this.field('someArr.$.someField').value

Perhaps this could be connected to the reactivity needed in #483.

[aldeed]

This could probably be added eventually, but it would actually be a change in the SimpleSchema package. Can you post this to that repo instead?