Feature request: import / export content rules

[Rudd-O]

Plone content rules are stored in an object IRuleStorage which is not visible in Zope space and is also not visible in content space (it can only be obtained using getUtility()). Implementation-wise, IRuleStorage is implemented as a simple OOBTree(), that can be acquired (plone.app.contentrules.browser.assignments.acquired_rules() has the scoop).

It would be great if the import/export framework had a step to deal with the rule storage. This would require at least a custom pair of serializer/deserializer.