message: API: Homogenize Course schema definition formatting
  (Only manual, local harmonization.)
diff: @@ -47,8 +47,7 @@ const courseSchema = new mongoose.Schema({
  type: mongoose.Schema.Types.ObjectId,
  ref: 'User'
  },
  - media:
  - {
  + media: {
  type: mongoose.Schema.Types.ObjectId,
  ref: 'Directory'
  },
  @@ -75,8 +74,8 @@ const courseSchema = new mongoose.Schema({
  },
  enrollType: {
  type: String,
  - 'enum': ['free', 'whitelist', 'accesskey'],
  - 'default': 'free'
  + enum: ['free', 'whitelist', 'accesskey'],
  + default: 'free'
  },
  whitelist: [
  {
  @@ -88,10 +87,12 @@ const courseSchema = new mongoose.Schema({
  type: mongoose.Schema.Types.ObjectId,
  ref: 'Picture'
  },
  - chatRooms: [{
  + chatRooms: [
  + {
  type: mongoose.Schema.Types.ObjectId,
  ref: 'ChatRoom'
  - }]
  + }
  + ]
  },
  {
  timestamps: true,
  