This first reverts the following 2 commits:
  566c0c5f
  3a08c758

to at least fix the issue that the context method takes 2 arguments that aren't
available from FormBoxEditor.edit() without slowing things even more.

About deferred style, widget editor objects can be ignored for the moment. If
we ever need to restore fully functional objects, the regression in commit
  a5a2f1cd
could be solved with the following patch:

--- a/product/ERP5Form/FormBox.py
+++ b/product/ERP5Form/FormBox.py
@@ -131,22 +131,32 @@ def render(self, field, key, value, REQUEST, render_prefix=None):
 class FormBoxEditor:
   """An editor returned from FormBox validation able to `edit` document."""
 
+  path = None
+
   def __init__(self, result, context):
     """Initialize with all necessary information for editing.
 
     Keep a reference to the correct context and don't expect the caller to provide it
     during the edit phase because they don't have access to the widget anymore.
     """
     self.attr_dict, self.editor_list = result
+    self.context = context
     self.edit = lambda _: self._edit(context)
 
   def __getstate__(self):
-    pass
+    return (self.attr_dict, self.editor_list,
+            self.path or self.context.getPhysicalPath())
+
+  def __setstate__(self, state):
+    self.attr_dict, self.editor_list, self.path = state
 
   def __call__(self, REQUEST):
     # Called by Base_edit in case of FormValidationError
     pass
 
+  def edit(self, context):
+    return self._edit(context.unrestrictedTraverse(self.path))
+
   def _edit(self, context):
     """Edit inside correct context."""
     context.edit(**self.attr_dict)

This commit also removes the unused view() method on editors.

/reviewed-on !622