According to MDLQA-140, a teacher can enable
guest access to a course.

According to MDLQA-139, a teacher can
enable self-enrolment in a course.

This commit removes any trace of the setting 'Completion tracking
begins on enrolment' as it does not appear to do anything.

course, cohort, enrol, role, groups and forum used to use hard-coded
MAX_USERS_PER_PAGE=100 for rendering user list. This has been converted
to $CFG->maxusersperpage.

MDL-37396 Enrollmen: pass $perpage as optional_param and set default perpage variable in quickenrolment.js

MDL-37410 External PHPunit test: used ->getDataGenerator()->enrol_user instead to manually enrol the user. + improve the unassignUserCapability to remove a capability assigned by getDataGenerator->enrol_users

YAY!

If the submit event listener is not correctly closed, then the submit event
calls the relevant callback multiple times incorrectly.

When hiding the Add role dialogue, we need to detach any event listeners
which are applied to it.

Credit goes to Tyron Delean, thanks.