[Delivers #68543726] Ensure custom column order is retained when adding a new row

Fixes a bug currently in the icebox: https://www.pivotaltracker.com/story/show/68543726

Perhaps this can wait till after our release is accepted/merged and I'll tweak this PR to be against the main archivesspace repo?

-----

New rows were not applying the custom order and were being inserted in the page with the default ordering.

Also fixed a labelling error in the Reorder form, where section labels were duplicating in the multiselect field if multiple sections existed for a column.