Remove site admins from provisioning list

Hi Spenser,
Just made a few minor alterations to our local version of the moodle plugin so that Site Admins etc are not included in the provisioning list unless they are already teachers in a course.
It creates a new capability which is granted to 'teacher' and 'editingteacher' role types on a course and then bases the Instructor role on that capability rather than on the moodle/course:update which includes admins etc.

Richard Oelmann
University of South Wales