[FR] Allow nested geos, dates and refs for import

[Volker Andres]

I am trying to import some data, but my data in the documents is nested. For example:

location: {
  geohash: 'xxx',
  geopoint: {
    _latitude: '...',
    _longitude: '...'
  }
}

When I try to import now with the following, it doesn't work. Would be very nice, if the restore function would traverse the JS-Object, when a "." is present.

firestoreService.restore('collections.json', {
    geos: ['location.geopoint'],
});

[Dale Nguyen]

Added in v0.6.0