Reorder fields in the InstructorForm, clean logic
Reorder fields in the InstructorForm, clean logic

Also:
* switched `super` calls to Python3
* removed unnecessary list-comprehension
* cleaner logic in required fields

pbanaszkiewicz/amy,swcarpentry/amy,swcarpentry/amy,vahtras/amy,swcarpentry/amy,vahtras/amy,vahtras/amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy