Dx siteroot

[mauritsvanrees]

Part of the dexterity site root PLIP.
The coding was done by @ale-rt but I did not see a PR.
The code seems good to me, and it works on a small test site.

[mister-roboto]

@mauritsvanrees 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!

[tisto]

LGTM

[ale-rt]

I started the jenkin jobs using the following parameters:

https://github.com/plone/Products.CMFPlone/pull/2612
https://github.com/plone/plone.app.contenttypes/pull/475
https://github.com/plone/plone.app.upgrade/pull/256