Added _lm_connection_get_server that returns the server string. The function uses the host part of the JID used, if it is not set the function will return a copy of the connect host. Also updated to use this internally in LmConnection as the same code was duplicated in a couple of places.

Mikael Hallendal <micke@imendio.com>
Dafydd Harries   <dafydd.harries@collabora.co.uk>
Senko Rasic      <senko.rasic@collabora.co.uk>