Adds support for special use case where the notification target is a …

…user

It is now possible to add new notifications like this:

notify_user($recipient_guid, $sender_guid, $subject, $body, [
    'action' => 'somea_action',
    'object' => $user, // <-- This parameter can now be ElggUser object
]);

start.php

@@ -176,6 +176,8 @@ function notifier_notification_send($hook, $type, $result, $params) {
 				// that it will get automatically mapped to the
 				// 'notifier/messages/create/relationship/friend' view.
 				$description = 'create:relationship:friend';
+			} else {
+				$entity = $object;
 			}
 
 			break;