Collective.contextimage

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- Nothing changed yet.

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- deliver default image resources always relative to navigation url
[jensens]

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- Use ``zope.interface.implementer`` and ``zope.component.adapter`` instead of
``zope.interface.implements`` and ``zope.component.adapts``.
[rnix]

- Return original order in base extender.
[rnix]

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- Add permissions for each schema extender and make extension fields editable
for Managers and Site Administrators.
[rnix]

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- Display condition for footer.
[espen]

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- Context image extension feature availability is now controlled by marker
interfaces.
[rnix]