Add common NGSI-LD constants

[jason-fox]

Add GeoProperty, Point , Date and Time types since GeoJSON is native in NGSI-LD.

NGSI-v2

The following provisioning statement is valid:

curl -L -X POST 'http://localhost:4041/iot/services' \
-H 'fiware-service: openiot' \
-H 'fiware-servicepath: /' \
--data-raw '{
  "services": [
    {
      "apikey": "4jggokgpepnvsb2uv4s40d59ov",
      "cbroker": "http://orion:1026",
      "entity_type": "Device",
      "resource": "/iot/d",
      "attributes": [
        {
          "object_id":"bpm",
          "type":"Float",
          "name": "heartRate"
        },
        {
          "object_id": "s",
          "name": "status",
          "type": "String"
        },
        {
          "object_id": "gps",
          "name": "location",
          "type": "geo:point"
        }
      ]
    }
  ]
}'

NGSI-LD

The following equivalent provisioning statement should be valid for NGSI-LD:

curl -L -X POST 'http://localhost:4041/iot/services' \
-H 'fiware-service: openiot' \
-H 'fiware-servicepath: /' \
--data-raw '{
  "services": [
    {
      "apikey": "4jggokgpepnvsb2uv4s40d59ov",
      "cbroker": "http://orion:1026",
      "entity_type": "Device",
      "resource": "/iot/d",
      "attributes": [
        {
          "object_id":"bpm",
          "type":"Property",
          "name": "heartRate"
        },
        {
          "object_id": "s",
          "name": "status",
          "type": "Property"
        },
        {
          "object_id": "gps",
          "name": "location",
          "type": "GeoProperty"
        }
      ]
    }
  ]
}'

but currently fails since GeoProperty is not defined as an exception and the default string value " " is not valid GeoJSON.

[jason-fox]

Note that it should be discussed if further additions should be required for LineString etc. I have not added them here because GeoProperty is a catch-all, however if necessary they should be added to #854

[fgalan]

Is there any other usage of LOCATION_TYPE and DATETIME_TYPE (removed in this PR) appart of the ones in this point?

[jason-fox]

Doesn't look like it, so those statements are now redundant and can be removed. Fixed 9d65c09

[fgalan]

LGTM

Shoud I merge? Or some other (with a better knowledge on NGSI-LD) should provide additional LGTM before that?

[jason-fox]

Please merge.