title: custom simple constraint grails
body: <p>I would like to create a custom simple constraint (like display and editable) which I can use within my Domain class. Is it possible to extend ConstrainedProperty class?</p>
  
  <pre><code>class City {
      String title
      BigDecimal latitude
      BigDecimal longitude
      Country country
  
      static constraints = {
          title       ( blank: false, customConstraint: true )  // filter can be also be applied as attributes: [customConstraint: true]
      }
  }
  </code></pre>
  
  <p>Somebody familiar with this case?</p>