Better admin hierarchy

items now get a full admin hierarchy including `alpha3` and `admin1_abbr`.

Note: any properties not contained in the schema definition should be considered transient as they will be discarded before writing to the database. (but can be used in the suggester-pipeline; for instance)

eg:
```javascript
{
  "id": 42455144,
  "center_point": {
    "lat": 40.874627800000006,
    "lon": -73.91183330000001
  },
  "name": {
    "default": "Marble Hill"
  },
  "type": "node",
  "tags": {
    "network": "Metro-North Railroad",
    "platforms": "1",
    "railway": "station",
    "source": "Yahoo",
    "wheelchair": "no",
    "wikipedia:en": "Marble Hill (Metro-North station)"
  },
  "alpha3": "USA",
  "admin0": "United States",
  "admin1": "New York",
  "admin1_abbr": "NY",
  "admin2": "New York",
  "local_admin": "Manhattan",
  "locality": "New York",
  "neighborhood": "Marble Hill"
}
```