Plone.app.z3cform

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- Use the more specific browser layer ``IPloneFormLayer`` for adapter
registrations. This avoids double registration errors.
[thet]

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- Integrate plone.app.widgets.
[vangheem]

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- Fix inline-validation warning error
[jbirdwell]

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- Handle an error where group.__name__ being None caused fieldsets to be given
the id 'fieldset-none', which causes issues the inline validation.
[esteele]

----------------

- Remove dependency on collective.z3cform.datetimewidget and instead use
plone.app.widgets.
[garbas, thet]

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- Translate fieldset labels correctly.
[maurits]

- We can add enable_unload_protection = False on a Form to disable unload protection.
[thomasdesvenain]

- Add '.empty' css class to fields that have no value.
[cedricmessiant]

- Indicate 'error' status when reporting errors from group forms.
[davisagli]

- Replace deprecated test assert statements.
[timo]

- Solve 13567: InlineValidation broken for MultiWidget.
[sunew]