schema: add locations

[ppanero]

Requires marshmallow-utils GeoJSONSchema merge and release inveniosoftware/marshmallow-utils#21
Closes #231

Important notes

• The ES mappings coordinates field inside the geometry is of typefloat, however it correctly stores the locations for both point and multipoint

"coordinates": {
    "type": "float"
}

indexed:

"locations" : [
              {
                "geometry" : {
                  "type" : "point",
                  "coordinates" : [
                    3.5480075,
                    165.577299
                  ]
                },
                "identifiers" : {
                  "wikidata" : "12345abcde",
                  "geonames" : "12345abcde"
                },
                "place" : "Naga",
                "description" : "Random place on land..."
              },
              {
                "geometry" : {
                  "type" : "multipoint",
                  "coordinates" : [
                    [
                      1.973974,
                      49.308415
                    ],
                    [
                      -9.508502,
                      -21.08845
                    ]
                  ]
                },
                "place" : "Losheim"
              }
            ],