entityList type media files should be treated as entity lists

[seadowg]

If a mediaFile in the manifest has a type attribute equal to entityList, the media file should be treated as an entity list. This means:

• Entity lists should be consistent between forms (as in Make sure that entity lists are consistent between follow up forms #6029)
• Registration and update forms should create/update entities locally (assuming other conditions for local entities are met)
• Entities in the list should be visible in the experimental entity browser

The manual route to creating local entity lists (through the entity browser) should still available for the moment to support users experimenting with entities using a server that does not support the type attribute yet.