Include compatibility for 'workflow_field' from 'workflow' module, v7.x-2.0

Problem/Motivation

As mentioned in https://www.drupal.org/node/2148935 the Workflow now includes Workflow Field. Now you can add a Workflow to terms, users or other entity types as you do with other Field types, and enjoy the features the Field API provides, such as revisioning, multilingual, etc.

As of now, if Workflow Field is used instead of Workflow Node you get the following error:

To set fields visibility you have to map the workflow to at least a content type.
There isn't a content type mapped to this workflow.

Proposed resolution

???

Interim tasks

Update the project description to specify that Workflow fields is not compatible with Workflow when workflow field is used.