quick frontend, primitivus, wix: MUC private messages management

/!\ not fully finished, backend part is not done yet /!\
    - as resources are discarded to manage chat windows lists, a pretty dirty hack is done to work around this:
      full jid is escaped using a prefix (it becomes invalid and resource is preserved).
    - new quick_utils module, with helper methods. escapePrivate and unescapePrivate implementations
    - MUC private messages are not managed in Wix yet

frontends/src/quick_frontend/quick_chat.py

@@ -21,7 +21,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from logging import debug, info, warning, error
 from sat.tools.jid  import JID
-
+from sat_frontends.quick_frontend.quick_utils import unescapePrivate
 
 
 class QuickChat():
@@ -110,6 +110,8 @@ class QuickChat():
 
     def _get_nick(self, jid):
         """Return nick of this jid when possible"""
+        if jid.startswith(const_PRIVATE_PREFIX):
+            return unescapePrivate(jid).resource
         return jid.resource if self.type == "group" else (self.host.contact_list.getCache(jid,'nick') or self.host.contact_list.getCache(jid,'name') or jid.node)
     
     def printMessage(self, from_jid, msg, profile, timestamp):