core: added a mechanism to associate short names to namespaces:

- new internal registerNamespace can be used by a plugin to associate a short name to a namespace
- new NamespacesGet bridge method retrieve those associations

src/plugins/plugin_misc_tickets.py

@@ -47,6 +47,7 @@ class Tickets(object):
     def __init__(self, host):
         log.info(_(u"Tickets plugin initialization"))
         self.host = host
+        host.registerNamespace('tickets', NS_TICKETS)
         self._p = self.host.plugins["XEP-0060"]
         self._s = self.host.plugins["PUBSUB_SCHEMA"]
         self._m = self.host.plugins["XEP-0277"]