core, bridge: added getFeatures method:

this async method indicate which plugins are activated, and add an additional data dictionary with plugin specific data.
    The result can be general (if profile==C.PROF_KEY_NONE) or specific to profile.

frontends/src/bridge/DBus.py

@@ -293,6 +293,15 @@ class DBusBridgeFrontend(BridgeFrontend):
             kwargs['error_handler'] = error_handler
         return self.db_core_iface.getEntityData(jid, keys, profile, **kwargs)
 
+    def getFeatures(self, profile_key, callback=None, errback=None):
+        if callback is None:
+            error_handler = None
+        else:
+            if errback is None:
+                errback = log.error
+            error_handler = lambda err:errback(dbus_to_bridge_exception(err))
+        return self.db_core_iface.getFeatures(profile_key, timeout=const_TIMEOUT, reply_handler=callback, error_handler=error_handler)
+
     def getHistory(self, from_jid, to_jid, limit, between=True, search='', profile="@NONE@", callback=None, errback=None):
         if callback is None:
             error_handler = None