Fix cut/copy & paste of many items

[petschki]

Save the cut/copy clipboard to request.SESSION because browser cookie length is restricted to 4096 bytes.

fixes #200

[mister-roboto]

@petschki 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

With this simple comment all the jobs will be started automatically.

Happy hacking!

[petschki]

@jenkins-plone-org please run jobs

[jensens]

Session is deprecated AFAIK, I do not think this one would work with Zope 5, right?

[mauritsvanrees]

In Plone 6 we don't have the session machinery anymore. You can still add it yourself. tempstorage had some problems, but that got fixed this year. Or use an alternative session implementation.

But sessions are not available by default in Plone 6, so I fear we should close this.