migrate all tests to use dexterity, fix most tests

[pbauer]

Sorry, I accidentally commited to master and had to revert in master. This reverts the revert.

There are currently three issues with this pull-request that will result in failing tests (at least in python3):

1. This fails at the moment since the ObjectAddedEvent of move-rule (test4) is triggered during container._setObject in _constructInstance:

   rval = container._setObject(id, obj)
   newid = isinstance(rval, six.string_types) and rval or id
   obj = container._getOb(newid)

   When the rule is executed the container changed and the object can no longer be found in the original container.

   For Archetypes the workaround was to delay the execution of the added action in handlers.added until IObjectInitializedEvent which we do not have :(
   See https://jenkins.plone.org/view/PLIPs/job/plip-py3/252/testReport/junit/plone.app.contentrules.tests.test_cascading_rule/TestCascadingRule/test_cascading_rule/

2. The sort-order of items in some tests is random. I do not know where this originates from. See https://jenkins.plone.org/view/PLIPs/job/plip-py3/252/testReport/junit/plone.app.contentrules.tests.test_configuration/TestGenericSetup/testExport/

3. The test test_action_mail.testExecute fails because of a weird issues with serialisation of text in emails. Maybe it is related to the MockMailHost. See https://jenkins.plone.org/view/PLIPs/job/plip-py3/252/testReport/junit/plone.app.contentrules.tests.test_action_mail/TestMailAction/testExecute/

[pbauer]

5.0 and 5.1 use branch 4.0.x of p.ap.contentrules, so I'm not sure why mr.roboto requires the jobs for 5.0 and 5.1 to run.
Since 5.2 is green I'll merge it and sill see if 5.0 and 5.1 are bothered by that.