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* Various improvements on buttons.
* Add support for error pages in SMI.
* Update to use ``silva.core.interfaces`` and directly ``five.grok``.
* SMI components are register on a SMILayer.
* The editor buttons (kupu editor, forms editor) can be disabled in
IDocument types that don't support a particular editor
(e.g. SilvaNews News Items don't support the forms-based editor)