Even as collective.cover has been in production using plone.app.contenttypes for more than 2 years in many sites, we haven't deal with testing that in CI.

Many changes were made here to achieve compatibility and fix some errors:

- testing content creation was refactored to simplify it
- Dexterity Image content was removed as is no longer necessary (test case is covered by using plone.app.contenttypes)
- a bunch of hacks to deal with Archetypes/Dexterity API incompatibilites were included
- RF collection tile test was refactored and finally fixed (I hope so)
- documentation was updated to include a known good versions of packages involved

This is a huge step in the search of Plone 5 compatibility.

We ignore some tests are randomly failing under Plone 4.2.