remove dependency on plone.app.referenceablebehavior

This pull-req removes the dependency on plone.app.referenceablebehavior, as it depends on Products.Archetypes which itself installs the uid_catalog.
With the plone.app.referenceablebehavior dependency in place, installing Plone 5 site will lead to a error, where plone.app.referenceablebehavior tries to get the uid_catalog.

For interoperability with Archetypes in a < Plone 5 environment, i suggest to either:
- document how to add the referenceablebehavior to Folder and any other content types, which need it,
- or to use a setup.py extra depencency section and do a setuphandler step, which adds this behavior to any needed p.a.contenttypes based types.