get the tests mostly running in plone 5

Here are proposed changes to get the tests running in Plone 5, given the adjustment I just made to plone.app.testing so that PLONE_FIXTURE does *not* install any content types.

This adds dependencies of the at and dx profiles on the profiles of the respective content type systems. This needs some discussion...

Depending on the Products.ATContentTypes profile is going to be problematic for compatibility with Plone 4 where it doesn't exist. Perhaps we can add an empty stub profile in ATContentTypes for those versions of Plone. Or another option would be to explicitly install the profile in the test setup rather than as a profile dependency, only in Plone >= 5.

Depending on the plone.app.contenttypes profile is also going to be problematic if that profile ends up depending on the p.a.e dx profile, creating a circular dependency. But I'm not clear on what we're doing there yet, so am ignoring this for now.

With this in place locally I have all but 4 tests passing. These 4 look like tests that are using the generic layer but actually do assume Archetypes content types are present. So they need to be adjusted to actually be generic, or moved to a test class that uses an AT layer.