Silva.core.interfaces

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* ...

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* Add an interface for services editable in SMI.

* Update some of the ghost interfaces.

* Update some of the quota interfaces.

* Add a bundle error, composed of multiple sub-errors.

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* Improve icon lookup API.

* Review API to set last author on contents.

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* Add an API ``IHTTPHeadersSettings``.

* Add a ``repair`` method to ``IOrderManager``.

* Fix some interface that were missing methods and attributes.

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* Update Silva XML import/export API.

* Renamed ``IAssetData`` to ``IAssetPayload``.

* Introduce an interface ``IReferable`` for content that can be
referred to (include ZMI objects).

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* Add ``ISilvaNameChooser`` to support a pluggable identifier
management.

* Extend ``IAuthorization`` to give access to related email.