Send XMPP Message through Stanza

Previously, when it sends XMPP info-query message, it sends in the
form of string. Now, it sends in more structured way through XML
stanza.

 - Two fields are added. One is data and the other is type.
 - Data field is intended for previously "<body>" for
 - Type field is for message types such as "send_msg", "con_req"
   and "con_resp"

NB. Previously, TinCan handles con_req and con_resp in the same way. 
(Even if TinCan sends con_resp through XMPP, it notifies to the controller 
it sends con_req). Now, you can differentiate these two message in your 
controller.(Though there is other way around to do it)