core: better handling of profile_key and don't write the param file anymore

- new error ProfileNotSetError and some methods use the default @NONE@ instead of @DEFAULT@
- do not output the .sat/param file anymore, it is not needed and created confusion
- plugin XEP-0054: remove an error message at startup

src/plugins/plugin_xep_0054.py

@@ -199,7 +199,8 @@ class XEP_0054(object):
 
     def vcard_err(self, failure, profile):
         """Called when something is wrong with registration"""
-        error(_("Can't find VCard of %s") % failure.value.stanza['from'])
+        if failure.value.stanza.hasAttribute("from"):
+            error(_("Can't find VCard of %s") % failure.value.stanza['from'])
         self.host.bridge.actionResult("SUPPRESS", failure.value.stanza['id'], {}, profile)  # FIXME: maybe an error message would be better
 
     def getCard(self, target_s, profile_key='@DEFAULT@'):