Autoscroll added, automatically moves to bottom of chat UIBubbleTableView when reloadData is called.

For me, I wanted my chat to scroll to bottom on arrival of a new message. Conveniently, this is when reloadData is called, so until a developer options list is made available, this seems like a great solution for most use cases.

If this would be better served as an optional parameter, I can code it up, just let me know.