Add a Plone 5 testing buildout configuration.
Declare missing dependency to collective.testcaselayer.
Disable plone.protect in tests.

This fixes some tests which were written when there was no plone.protect on links,
such as the Edit link.
Fix copy/paste test by not using folder contents.

Folder contents seems to have changed a lot in Plone 5.
Merge branch 'jone-plone-5-tests'