lib: Introduce Response::setRerenderLayout()

Instead of handling response headers based on flags in our controllers, this should happen in the request for usage w/o controllers.

refs #9660

library/Icinga/Web/Response.php

@@ -15,6 +15,13 @@ class Response extends Zend_Controller_Response_Http
      */
     protected $request;
 
+    /**
+     * Whether to send the rerender layout header on XHR
+     *
+     * @var bool
+     */
+    protected $rerenderLayout = false;
+
     /**
      * Get the request
      *
@@ -28,6 +35,39 @@ class Response extends Zend_Controller_Response_Http
         return $this->request;
     }
 
+    /**
+     * Get whether to send the rerender layout header on XHR
+     *
+     * @return bool
+     */
+    public function getRerenderLayout()
+    {
+        return $this->rerenderLayout;
+    }
+
+    /**
+     * Get whether to send the rerender layout header on XHR
+     *
+     * @param   bool $rerenderLayout
+     *
+     * @return  $this
+     */
+    public function setRerenderLayout($rerenderLayout = true)
+    {
+        $this->rerenderLayout = (bool) $rerenderLayout;
+        return $this;
+    }
+
+    /**
+     * Prepare the request before sending
+     */
+    protected function prepare()
+    {
+        if ($this->getRequest()->isXmlHttpRequest() && $this->getRerenderLayout()) {
+            $this->setHeader('X-Icinga-Rerender-Layout', 'yes');
+        }
+    }
+
     /**
      * Redirect to the given URL and exit immediately
      *
@@ -54,4 +94,13 @@ class Response extends Zend_Controller_Response_Http
         $this->sendHeaders();
         exit;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function sendHeaders()
+    {
+        $this->prepare();
+        return parent::sendHeaders();
+    }
 }