refactor form error handling:
* almost everything is in the base form class, with other form errors related code
* deprecate form_field_error in favor of field_error and format_error on the renderer
* fix pb with js localization of errors by properly using field.role_name()
* rename 'errors' into 'error' in forminfo to avoid confusion
This directory is where you should put your lax components.
For your application to actually use a component, you also
have to modify the ``INCLUDED_COMPONENTS`` variable in
the ``custom.py`` module.