Z3c.formui

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- Bug: Fixed up meta-data and the release.

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- Feature: Added subform content and layout template. This allows you to
configure real sub forms which do not render the form tag.

- Feature: Improve layout implementation, support built-in layout templates.

- Feature: Use ``IContentTemplate`` instead of ``IPageTemplate`` in layout
base classes. This will help to prevent running into recursion errors if
there is a missing layout template.

- Feature: Added form module which offers built-in layout support.

- Bug: Added missing display ``IContentTemplate``, otherwise we can run into a
recursion in some cases.

- Bug: Renamed table macro argument from ``form-required-info`` to
``required-info``. The macro ``form-required-info`` did not exist.

- Bug: Added unit tests for layout support.

- Bug: Added tests for layout macros.

- Bug: Added tests for layout templates.

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- Refactoring: Update CSS classes to reflect latest changes to the widget
classes in ``z3c.form``.

- Bug: Error view snippets may have a empty ``widget`` attribute values, so we
cannot rely on accessing the label of the widget. This is the case, if the
error view sniipet was created from an invariants validation error.

- Bug: The table-form template did not properly render the error at the
widget, because the ``render()`` method was not called. Thanks to Markus
Leist for the report.

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- Feature: The row div element now also has an id of the form
"<widget-id>-row".

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- Refactoring: Split up registrations for simpler management of UI
components. This also makes it easier to see for developers how to create a
new template for forms.

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- Feature: Registered all defined macros for each form template. Also, added
more slots to the templates providing more hooks for customization.

- Feature: Added a macro/slot for the "required info", which explains how
required fields are marked.

- Feature: Added support for form labels.

- Feature: Added support for groups to templates.