In `bp_notifications_get_notifications_for_user()` set the `$notification_object` as the `$component_action_item[0]` object rather than an empty stdClass. This maintains backwards compatibility with existing functionality, while allowing groups of notifications to have a bit more metadata to play with on output.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8745 cdf35c40-ae34-48e0-9cc9-0c9da1808c22