Dar 120 - wall empty bug fix

Currently the data for Wall/Forum is inconsistent, as the entries in comments_index table are created in a separate db transaction, and when this second transaction fails, we end up having posts attached to 'Empty'. In this pull requests I've added a hook triggered when an article is saved. In case it's a Wall or Forum post, the comments_index row is added within the transaction that is used to create the post.