core: dynamics menus refactoring:

- menu now use generic callback system, with extra data
    - asyncMenuCall is removed in favor of launchAction
    - menu_id (== callback_id) is used to identify menu instead of category/name/type tuple
    - i18n is managed throught deferred translation, and returned with _i18n suffix
        e.g.: menu (D_('File'), D_('Open')): (u'File', u'Open') is menu_path, (u'Fichier', u'Ouvrir') is french menu_path_i18n.
    - type actually can have the following values:
        - NORMAL: classical menu
        - JID_CONTEXT: contextual menu, used with any jid
        - ROSTER_JID_CONTEXT: like JID_CONTEXT, but restricted to jids in roster.
        - ROSTER_GROUP_CONTEXT: contextual menu, use with groups
    - security_limit is used, in the same way as for parameters
    - when using importMenu, callback can be an actual callback, or one already registered with registerCallback

frontends/src/constants.py

@@ -58,3 +58,5 @@ class Const(object):
     # from plugin_misc_text_syntaxes
     _SYNTAX_XHTML = "XHTML"
     _SYNTAX_CURRENT = "@CURRENT@"
+
+    NO_SECURITY_LIMIT = -1