Validate functions should be called with useful properties

[Macrofig]

Need to at least pass new value and property key name to the resulting compute of a validate property function.

For example, the following define property:

myVal: {
  type: 'string',
  validate: {
    required: function () {
      return this.attr('isRequired') || false;
    },
    validateOnInit: true
  }
}

The required function should have the new value and the property name in the arguments. So...

    required: function (newVal, key) {
      return this.attr('isRequired') || false;
    },