title: Knockout Validation: how to validate the fields on button click, not on input change
body: <p>I'm using the following knockout validation plugin: <a href="https://github.com/Knockout-Contrib/Knockout-Validation" rel="noreferrer">https://github.com/Knockout-Contrib/Knockout-Validation</a></p>
  
  <p>I want to validate my fields when I click on the "Submit" button, not everytime when I change the input's value. How can I do that?</p>
  
  <p>Javascript:</p>
  
  <pre><code>ko.validation.init({
      insertMessages:false,
      messagesOnModified:false,
      decorateElement: true,
      errorElementClass: 'wrong-field'
  }, true);
  
  var viewModel = {
      firstName: ko.observable().extend({minLength: 2, maxLength: 10}),
      lastName: ko.observable().extend({required: true}),
      age: ko.observable().extend({min: 1, max: 100}),
      submit: function() {
          if (viewModel.errors().length === 0) {
              alert('Thank you.');
          }
          else {
              alert('Please check your submission.');
              viewModel.errors.showAllMessages();
          }
      },
  };
  
  viewModel.errors = ko.validation.group(viewModel);
  
  ko.applyBindings(viewModel);
  </code></pre>
  
  <p>HTML:</p>
  
  <pre><code>&lt;fieldset&gt;    
      &lt;div class="row" data-bind="validationElement: firstName"&gt;
          &lt;label&gt;First name:&lt;/label&gt;
          &lt;input type="text" data-bind="textInput: firstName"/&gt;
      &lt;/div&gt;
  
      &lt;div class="row" data-bind="validationElement: lastName"&gt;
          &lt;label&gt;Last name:&lt;/label&gt;
          &lt;input data-bind="value: lastName"/&gt;
      &lt;/div&gt;
  
      &lt;div class="row"&gt;
          &lt;div class="row"&gt;
              &lt;label&gt;Age:&lt;/label&gt;
              &lt;input data-bind="value: age" required="required"/&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  &lt;/fieldset&gt;
  
  &lt;fieldset&gt;
      &lt;button type="button" data-bind='click: submit'&gt;Submit&lt;/button&gt;
      &amp;nbsp;
  &lt;/fieldset&gt;
  </code></pre>
  
  <p>This is my jsfiddle: <a href="http://jsfiddle.net/xristo91/KHFn8/6464/" rel="noreferrer">http://jsfiddle.net/xristo91/KHFn8/6464/</a></p>