Navigation: Add method merge()

refs #5600

library/Icinga/Web/Navigation/Navigation.php

@@ -269,6 +269,24 @@ class Navigation implements ArrayAccess, Countable, IteratorAggregate
         return new RecursiveNavigationRenderer($this);
     }
 
+    /**
+     * Merge this navigation with the given one
+     *
+     * Any duplicate items of this navigation will be overwritten by the given navigation's items.
+     *
+     * @param   Navigation  $navigation
+     *
+     * @return  $this
+     */
+    public function merge(Navigation $navigation)
+    {
+        foreach ($navigation as $item) {
+            $this->addItem($item);
+        }
+
+        return $this;
+    }
+
     /**
      * Create and return a new set of navigation items for the given configuration
      *