All Form box use by default invisible css class

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@31113 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/FormBox.py

+# -*- coding: utf-8 -*-
 ##############################################################################
 #
 # Copyright (c) 2002-2006 Nexedi SARL and Contributors. All Rights Reserved.
@@ -86,6 +87,14 @@ class FormBoxWidget(Widget.Widget):
                                 default="",
                                 required=0)
 
+  css_class = fields.StringField('css_class',
+                                  title='CSS class',
+                                  description=(
+      "The CSS class of the field. This can be used to style your "
+      "formulator fields using cascading style sheets. Not required."),
+                                  default="invisible",
+                                  required=0)
+
   def render(self, field, key, value, REQUEST, render_prefix=None):
     """
         Render a form in a field