implement Double-Opt-In

CRM/Twingle/Form/Profile.php

@@ -336,6 +336,13 @@ class CRM_Twingle_Form_Profile extends CRM_Core_Form {
       array('class' => 'crm-select2 huge', 'multiple' => 'multiple')
     );
 
+    $this->add(
+       'checkbox', // field type
+       'double_opt_in', // field name
+       E::ts('Use Twingle\'s Double-Opt-In procedure'), // field label
+       FALSE // is not required
+     );
+
     $this->add(
       'select', // field type
       'postinfo_groups', // field name