add option to label formatter to show labels without considering user access

Entityreference fields are frequently used to classify other entities. Now that it's simple to create custom entity types (with modules such as ECK, or Entity API), it's often desirable to use a custom entity type for this sort of thing, rather than Taxonomy terms.

For example, suppose I am building a schedule for a DrupalCamp website. I want to classify sessions into rooms and tracks. I may want to create a custom entity type for either rooms or tracks, rather than use taxonomy.

However, this causes a problem:

* editor users should be able to view a room or track entity, so they can work with it
* normal users have no need to view a room or track entity
* normal users DO need to see on a session node the room and track reference it belongs to: ie, the value of the reference field as an entity label.

So we have a problem in that Drupal's entity system doesn't distinguish between 'view the whole entity' and 'view the entity's label in an embedded context'.

Taxonomy has always got round this by simply using the same view access as nodes: if you can see a node, you can see a term.

However, for custom entities, this isn't possible.

Given that it's not feasible at this stage to completely rework the way entity access works with some sort of extra 'view label' permission, I think the best thing is to add an option to the 'label' formatter to bypass the entity access control.

This would give let site builders determine when it's appropriate to show labels. For example, in the camp schedule example, the site builder would know that it's part of the design to allow users to see the names of rooms, even without letting them access the full room entities.