Specify hipchat server address

Add an ability to connect to self managed HipChat Server.

I left this part intact because the domain part of user's jid is always `chat.btf.hipchat.com` in HipChat Server, and it is still in beta state so this behavior might change in the future. Users can still connect to the server specifying full form of jid, e.g. `user@chat.btf.hipchat.com` to `config.adapters.hipchat.jid`