Disable/Re-enable a course's 'lti_contexts' when course is archived/unarchived

Since the lti_contexts table is global and not course specific, it's not part of the archival/unarchival process. We need to at least disable class list and grade sync when archiving. Nice to have would be re-enabling the auto syncs when unarchiving, but this also assumes the Canvas side hasn't changed, so maybe not as important. Requires #49 