In the edit profile view, when showing the date of a successful OPML export, try to show the export_date field.

Only if the export_date field is nil, use the rails-maintained updated_at field. This should never happen if model validations work correctly, but there could be old db records from before the export_date column was added to the opml_export_job_states table which would show this behavior.

Complementary to 69fd9153e8b1933f50711b528eb38eca3a92ff72