Add a new behavior to link images on a risk

[ale-rt]

This is an MVP for the image selection widget in the risk edit form.

Requires the following checkouts:
We do not require them anymore because updated eggs they have been released in the meanwhile.

[sources]
# plone.app.content = git git@github.com:plone/plone.app.content.git branch=master
# plone.app.z3cform = git git@github.com:plone/plone.app.z3cform.git branch=master
# plone.z3cform = git git@github.com:plone/plone.z3cform.git branch=ale/29/fix

I would not merge this one yet because there is still quite a lot to do.

About image management

• I could not find in proto how to add a new image, I had to add the images manually
  (calling /++add++Image)
• There is no clear way to manage uploaded images (editing, deleting, ...)

About the relation management:

• Only one relation can be picked at a time
• Removing a relation is not yet implemented
• When sorting the relations some injection happens (it should not)
• When sorting the relations the images are (apparently) not sorted,
  but reloading the page shows them in the proper order

Minor UI issues:

• The picker that opens in the panel has not the proper classes in the buttons
• We do not have a proper macro for the tabbed panels
• There is no page to display the image view
• In the navigation tree we do not have an icon for the image

Rest API issues:

• The related_images field is not serialized as null

[pilz]

I passed the missing image upload to D.

[pilz]

I tried that out, upgrade steps ran fine, works as described. Code style wise, I am no authority, but trust. Looks fine.

[mauritsvanrees]

I requested two small technical changes.
With those addressed, it works for me.

But there are still the points that Alessandro already mentions. Main ones being: there is no way in Proto to upload an image, and removing a related image is not yet implemented.

This also means that basically the entire Plone Site is now an image bank: the tool presents any Image it finds anywhere. Probably they should be somewhere central. But that probably means the image bank app itself should be implemented first. Or am I missing something?

So this is a good start, but it may only be mergeable once work in other areas is done.

[mauritsvanrees]

Thanks, the changes are good. I have left another suggestion, but it is that: a suggestion.

Technically I would approve, but there are still the open questions, mostly for Alex to consider.

All required changes have been made.

[ale-rt]

Thanks, the changes are good. I have left another suggestion, but it is that: a suggestion.

Technically I would approve, but there are still the open questions, mostly for Alex to consider.

CC @pilz, see also the issue description