This patch includes following changes and new features:
* Group sync in enrol_cohort plugin.
* Option for editing of role in existing cohort sync instance.
* Group memberships are now restored after enrolments.
* New enrol method for restore of protected group membership.
* New component callback 'restore_group_member' for restore of general plugin group membership.
* New component callback 'restore_role_assignment' for restore of general plugin role assignments.
* Implemented group membership protection in enrolment UI.
* Other minor fixes and cleanup.

Notes:
* The YUI base enrolment page is not reimplemented yet - see MDL-35618.