Allow multiple value entity reference fields to use formatter

Problem/Motivation

There are plenty of times when site builders would want a list of entity reference fields, not just text, using all the formatter options.

Proposed resolution

Add entity reference fields as a field type that can use the formatter. Entity fields are sometimes links to the entity and sometimes just the plain title so there should be an option to select which way to display them.

User interface changes

• Anywhere an entity reference field can use a field formatter, this one will be an option.
• An additional formatter option will allow selection of plain text title or link to entity.