ERP5Form,Formulator: make widget a new style class

This makes consistent method resolution order with python3 and reveal a
problem that relation field widgets render_pdf was not the expected one
on python3, solve this by defining explicitly the method.

product/ERP5Form/MultiRelationField.py

@@ -367,6 +367,8 @@ class MultiRelationStringFieldWidget(Widget.LinesTextAreaWidget,
       )
     return html_string
 
+  render_pdf = Widget.LinesTextAreaWidget.render_pdf
+
   def render_autocomplete(self, field, key):
     """
     Use jquery-ui autocompletion for all relation fields by default, requiring

product/Formulator/Widget.py

@@ -86,7 +86,7 @@ def convertToString(value):
     return str(value)
   return value
 
-class Widget:
+class Widget(object):
   """A field widget that knows how to display itself as HTML.
   """