The ILeadImage inherits from IImageScaleTraversable to enable the ima…

[ale-rt]

…ges view

Fixes #576

[mister-roboto]

@ale-rt thanks for creating this Pull Request and help improve Plone!

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass.

Whenever you feel that the pull request is ready to be tested, either start all jenkins jobs pull requests by yourself, or simply add a comment in this pull request stating:

@jenkins-plone-org please run jobs

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Happy hacking!

[ale-rt]

This can be tested TTW by using the plips/plip-2454-dx-siteroot.cfg in buildout.coredev, enabling the leadimage behavior on the Plone site and adding an image.
Without this patch the view of the Plone site will be broken as described in #576.

[ale-rt]

@jenkins-plone-org please run jobs

[jensens]

Seems legit at a first look. And that said the question is, if we want to make all places where image fields are used explicit traversable:

At the moment this is set to all DX content - anyway if it has an image or not.
https://github.com/plone/plone.app.dexterity/blob/41498dc5113aeb465b31c816c9e8b369739a087c/plone/app/dexterity/configure.zcml#L49

Problem will occur on plone.supermodel (XML/TTW) based image fields then.
So this is not an option.
Ergo: I would add the <implements... as above for the site root instead of subclassing in the ILeadImage.