title: datepicker works on widgets options page, but not on customizer
body: <p>I have a widget with a date option field, which works correctly when in the dashboard, but fails to display when on the theme customizer.</p>
  <p>I declare the field for the in the form() method like this (one input field for the date-picker, and another for the altField):</p>
  <pre class="lang-php prettyprint-override"><code>$form .= '&lt;span class=&quot;widget-field&quot;&gt;';
  $form .= sprintf(
          '&lt;label for=&quot;%1$s&quot;&gt;%2$s&lt;/label&gt;&lt;input type=&quot;text&quot; data-type=&quot;date&quot; id=&quot;%1$s&quot; name=&quot;%3$s&quot; value=&quot;%4$s&quot; class=&quot;date-picker widefat&quot; &gt;',
          $this-&gt;get_field_id( 'start-date-picker' ),
          __( 'From:', 'yosilosetheme' ),
          $this-&gt;get_field_name( 'start-date-picker' ),
          $start_v );
  
  $form .= sprintf(
          '&lt;input type=&quot;hidden&quot; id=&quot;%1$s&quot; name=&quot;%2$s&quot; value=&quot;%3$s&quot; class=&quot;realdata-date-picker widefat&quot; &gt;',
          $this-&gt;get_field_id( 'start-date' ),
          $this-&gt;get_field_name( 'start-date' ),
          $instance['start-date'] );
      $form .= '&lt;/span&gt;';
  </code></pre>
  <p>In 'admin_enqueue_scripts&quot; I enqueue jquery-datepicker and get the styles using:</p>
  <pre class="lang-php prettyprint-override"><code>wp_register_style('jquery-ui', 'http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/jquery-ui.css');
  wp_enqueue_style( 'jquery-ui' );
  </code></pre>
  <p>and</p>
  <pre><code>wp_register_script( $this-&gt;_token . '-settings', esc_url( $this-&gt;assets_url ) . 'js/settings.js', array( 'jquery', 'jquery-ui-core', 'jquery-ui-datepicker' ), $this-&gt;_version );
  wp_enqueue_script( $this-&gt;_token . '-settings' );
  </code></pre>
  <p>settings.js holds this to look up the datepicker fields and activate them:</p>
  <pre class="lang-js prettyprint-override"><code>$('body').on('focus', &quot;.date-picker&quot;, function () {
      $(this).datepicker(
          $.extend({
                  altField: $(this).parent().find('.realdata-date-picker'),
                  altFormat: 'yymmdd'
              },
              $.datepicker.regional['es'])
      );
  });
  </code></pre>
  <p>Again, this all words perfectly and as expected on the Dashboard, but it won't display the calendar in the theme customizer. I see that all the appropriate files are being loaded (jquery, jquery-ui styles, datepicker.js, etc.); and on the debugger I can see that when focusing on these fields it does trigger the datepicker() call... but still nothing.</p>
  <p>(Wordpress 4.1)</p>