Function to get latest activity feed post for a record

@joep Not sure if one such exists, but to the best of my knowledge it doesn't and one of the ways to achieve it is to store a feed entry for the corresponding case always in database entity and update it on need basis(for instance when ever a new feed entry is made for corresponding case). In this way we can make sure that we can make sure that we are posting comments to latest feed entry as long as we are making use of processes to post comments or hazards. Let's see if any other practitioners comes up with better suggestions.