generic datamodel for chillhub+devices

A way to represent a datamodel on Firebase.

Inspired by what found in Firebase Datasets: https://www.firebase.com/docs/open-data/transit.html#section-data-structure

This datamodel is supposed to be generic and should work for chillhub and any connected devices.

main changes:

* a fridge container will list in `objects`, the different devices connected to it.

Those devices could be containers or objects.
For example, In the case of a beerminder, it should be a container with an array of objects to beers.

* containers should have `compType` to defined which type of container they are

I think this works. However, your sample data (second push) now has `container` entries that violate this schema:
```json
    "-he6ke7hocc" : {
      "compType" : "beerminder_container",
      "name" : "Beerminder_firstbuild",
      "objects" : {
        "-JUAwerASDvas-1g12j" : true,
        "-JUG7T_C4iVFZMMPjCB0" : true
      },
      "parent" : "-JUApygMzgusoiSlvV-0"
    }
```