title: Add website field using event observer in magento admin role permissions
body: <p>I'm creating a module that allows the user to choose the website during creating a role permission (System -> Permission -> Role -> Add New role -> Role Resource). I'm using an observer to achieve this, however I cannot get the form object.</p>
  
  <p><strong>Observer.php</strong></p>
  
  <pre><code>class Mymodule_Mycompany_Model_Observer 
  { 
      public function appendCustomRow(Varien_Event_Observer $observer)
      {
          $block = $observer-&gt;getEvent()-&gt;getBlock();
          if (!isset($block)) {
              return $this;
          }
          if ($block-&gt;getType() == 'adminhtml/permissions_editroles') {       
              //get form instance
              $form = $observer-&gt;getEvent()-&gt;getForm();
              //create new custom fieldset 'website'
              $fieldset = $form-&gt;addFieldset('website', array(
                  'legend' =&gt; 'Website Extras',
                  'class' =&gt; 'fieldset-wide'
                  )
              );
              //add new field
              $fieldset-&gt;addField('website', 'text', array(
                  'name'      =&gt; 'website',
                  'label'     =&gt; Mage::helper('adminhtml')-&gt;__('Website'),
                  'title'     =&gt; Mage::helper('adminhtml')-&gt;__('Website'),
                  'disabled'  =&gt; false,
              ));
          }
      }
  }
  </code></pre>
  
  <p><strong>Mymodule/Mycompany/etc/config.xml</strong></p>
  
  <pre><code>&lt;adminhtml&gt;
           &lt;events&gt;
              &lt;core_block_abstract_prepare_layout_before&gt;
                  &lt;observers&gt;
                      &lt;Event_column_append&gt;
                          &lt;type&gt;model&lt;/type&gt;
                          &lt;class&gt;Mymodule_Mycompany_Model_Observer&lt;/class&gt;
                          &lt;method&gt;appendCustomColumn&lt;/method&gt;
                      &lt;/Event_column_append&gt;
                  &lt;/observers&gt;
              &lt;/core_block_abstract_prepare_layout_before&gt;
            &lt;/events&gt;
  &lt;/adminhtml&gt;
  </code></pre>