Added interface for displayed last message, TXCFriendCell refactored

I added basic interface for displaying of the last message in friend list. I refactored TXCFriend class.
But I didn't implement part with some noting of the last message (for example orange pin, like in skype).
Also i didn't test my solution on a group chat, because I have  symmetric NAT and I can't connect with GroupBot.
Also I don't know how to use the storyboard, and I added all the interface to a cell with coding. I thing that is not the best solution,and so implementation is up on you if you can offer something better.