Option to pass an EntitySet with 2+ entities, and normalize one of them

Add functionality such that an entity in an EntitySet with more than one entity can be normalized.

- user specifies which entity they want normalize
- new EntitySet is created where that entity is normalized, all other entities are present, and existing relationships are preserved (but edited so that matches up with the newly created entities due to normalization)

- idea: possibly be able to normalize all non-normalized entities that are in the EntitySet at once