trim tag values

[Peter Johnson]

we should trim tag keys and values as there are some errors in the vancouver extract data such as (note the leading space for ice_cream) which will be common in the OSM data in general:

  "2757646809": {
    "id": 2757646809,
    "type": "node",
    "lat": 49.312619700000006,
    "lon": -123.14273030000001,
    "tags": {
      "amenity": " ice_cream",
      "source": "local_knowledge"
    },
    "timestamp": "2014-04-01T04:32:43Z"
  },

note: I fixed OSM https://www.openstreetmap.org/changeset/31043074