Add the ability to add creator object editors on bulk issue add

[adam-knights]

This PR add the ability to use creator objects for editors when adding multiple issues in one go. I believe this fills the last gap of screens where using creator objects was not available.

It also fixes a small bug I noticed in testing, where currently age rating and no age rating were on the form, but were not persisted.

Testing:
Tested locally with a variety of editors, including credit description. Tested submit, approve and view. Tested validation when no credit description. Example testing screenshots below.

[jochengcd]

Did you run flake8 on it ? Seems lines are longer than 80 chars ?

[adam-knights]

I did not - I'm still getting used to python, but it is growing on me, so flake8 was new. I've now used it here, and will for future contributions.