Implemented writeAll and closeAll for groups

src/Group/GroupManager.php

@@ -44,5 +44,11 @@ class GroupManager implements EventEmitterInterface
         return $group;
     }
 
+    public function closeAll(string $reason, int $code=1001)
+    {
+        foreach ($this->groups as $group) {
+            $group->closeAll($reason, $code);
+        }
+    }
     
 }