[ticket/12270] Corrent post and topic approval notification message

When you submit a post with needed approval (say user A), and then
it gets approved by another user (user B), a subscribed user (user C)
to that forum would receive a notification indicating:
-A has replied to topic 'New Topic' in the forum 'xyz'.
The expected result would be:
-A has posted a new topic 'New topic' in the forum 'xyz'.
This has fixed by adding a TOPIC_ID template variable to
mcp_post.html and, in there, depending if the first post is the topic's
first post or not, add a input's with name topic_id_list[] or
post_id_list[] and then the respective value (TOPIC_ID or POST_ID).

PHPBB-12270