Fixes in EAD bioghist import/export, refs #7124 (updates #7 and #8)

- Don't add empty bioghist elements in EAD export
- Don't create new 'Untitled' actors if bioghist value match
  the history value of the creator in the same position
- Improve comments showing different options on import
Are we checking somewhere for when the actor name, history, and repository match? Re: Dan's comment: " if the actor and repo AND bioghist is the same, it will just link, and no duplicate will be created"