Repeating elements

This issue is about how to represent repeating elements in this schema and ultimately in Mongoose.

## "Repeating elements"?

The definition of a "repeating element" is given in the MetaDefinitions table of the Data Dictionary:

> "[type]" Indicates that a field may be repeated and will include a defining string that indicates the instance of the repeated element. Such that Room[type]Features becomes RoomKitchenFeatures and refers to the Features of the Kitchen.

Here are some of the Room repeating elements from the Property resource:

> ### RoomType *String List, Multi*
This field is a list of the types used in the rooms repeating elements.  The Type is a list of possible room types.  i.e. Bedroom, Bathroom, Living Room, Workshop, etc. Each selected are expected to appear as the "[type]" in the related rooms fields. Note that Garage or Basement should not be added as a room type and are represented by the ParkingFeatures and Basement fields respectively.

> ### Room[type]Area *Number*
[type] This field is a repeating element for each type of room selected in the RoomType field. For every enumeration selected in the RoomType field, add an iteration of this field replacing [type] with the value from RoomType. The total area of the room. Use the RoomAreaUnits for the units of measurement used in this field.

I think what this means is that a document with repeating room elements would have an object representation something like this:

```js
{
  /* ... */
  RoomType: ['Kitchen', 'MasterBathroom'],
  RoomKitchenArea: 150,
  RoomKitchenAreaUnits: 'Square Feet',
  RoomKitchenAreaSource: 'Agent',
  RoomKitchenDimensions: '20 x 7.5',
  RoomKitchenLength: 20,
  RoomKitchenWidth: 7.5,
  RoomKitchenLengthWidthUnits: 'Feet',
  RoomKitchenLengthWidthSource: 'Agent',
  RoomKitchenLevel: 'Main',
  RoomKitchenFeatures: ['Double Sink', 'Stainless Steel Appliances'],
  RoomKitchenDescription: '...',
  RoomMasterBathroomArea: 40,
  RoomMasterBathroomAreaUnits: 'Square Feet',
  RoomMasterBathroomAreaSource: 'Agent',
  RoomMasterBathroomDimensions: '8 x 5',
  RoomMasterBathroomLength: 8,
  RoomMasterBathroomWidth: 5,
  RoomMasterBathroomLengthWidthUnits: 'Feet',
  RoomMasterBathroomLengthWidthSource: 'Agent',
  RoomMasterBathroomLevel: 'Main',
  RoomMasterBathroomFeatures: ['Glass Enclosed Shower', 'Heated Autonomous Robot Bidet', 'Guest WiFi'],
  RoomMasterBathroomDescription: '...'
  /* ... */
}
```

Unfortunately I don't think we can represent this kind of free-form-ish schema without modifying Mongoose internals, which assumes a consistent schema for all instances of a type (not unreasonable—that's the idea of types).

Alternately, we can generate a schema that already includes all of the fields for each enumeration of each RepeatingElement, but this is a really large number of optional elements.

## TODO

- [ ] Figure out what to do
- [ ] Do it

@slajax what about group?