message: Group progresses by unit
diff: @@ -39,7 +39,8 @@ export class ReportController {
  // TODO: Add group by unit for progress objects
  const progressPromise = Progress.aggregate([
  - {$match: { course: new ObjectId(id) }}
  + {$match: { course: new ObjectId(id) }},
  + {$group: { _id: '$unit', progresses: { $push: '$$ROOT' }}}
  ]).exec();
  const promises: Promise<any>[] = [
  coursePromise,
  