Added command /roster full.

Now /roster full command behaves like /roster before. /roster prints just a plain list
of nicks. This is good for smaller screens and convenient.

If you want you can review it and merge. For me this is more convenient way to see contacts in a roster, and I think this can be also better for some people. 

I am not a C programmer, so you probably can expect some silliness in this code.