Silva-core-layout

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* ...

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* Fix an Acquisition bug in the metadata helper for layouts.

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* Change doctype of the Porto layout to HTML 5. If you inherit from
this layout, and don't change the main layout, you can override with
the doctype attribute from the class.

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* Update Zope API calls.

* Fix a bug on error pages.

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* Version are now rendered with a layout if directly called. You need
to have the permission ``Read Silva content`` to access them.

* Default Porto templates are now written with ``grokcore.chameleon``.

* Various Silva 3.0c1 API updates.

* Improve tests.

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* The default page to render a content now does itself, without
delegating with the content object. This makes things much more
cleaner. ``request.model`` is no longer
supported. ``request.resourcebase`` as well.

* Use silva.fanstatic to include resources. Now use fanstatic
packaging for jquery and jqueryui.

* Now use the generic package ``grokcore.view`` instead of
``infrae.layout``.

* Support for the legacy layout is no longer supported and have been
removed.