core, memory, bridge, plugin misc_register_account: move registerNewAccount to a new plugin:

- the bridge method has been removed, now a plugin takes care of it with XMLUI callback system
    - TODO: xmpp.RegisteringAuthenticator still needs to be fixed

src/memory/params.py

@@ -135,7 +135,6 @@ class Params(object):
         self.default_profile = None
         self.params = {}
         self.params_gen = {}
-        host.registerCallback(host.registerNewAccountCB, with_data=True, force_id="registerNewAccount")
 
     def asyncCreateProfile(self, profile):
         """Create a new profile