Allow Multiple Evaluators for a Course

**Is your feature request related to a problem? Please describe.**
At present, only a single Evaluator can be specified for a Course.
This scenario does not work well for many training situations.
In many workplaces there are multiple evaluators for a Course.
In some workplaces "students" can become evaluators once they have successfully passed the same course and are considered competent to assess others.

**Describe the solution you'd like**
Change the field to allow multiple Evaluators.
Allow the addition of a students who have passed the course to be selectable as Evaluators

**Describe alternatives you've considered**
Use another LMS.

**Additional context**
None