Add imposm config to expose airport codes

Author: Rub21

images/tiler-imposm/config/layers/transport_areas.json

@@ -41,6 +41,26 @@
           "name": "class",
           "key": null
         },
+        {
+          "type": "string",
+          "name": "ref",
+          "key": "ref"
+        },
+        {
+          "type": "string",
+          "name": "iata",
+          "key": "iata"
+        },
+        {
+          "type": "string",
+          "name": "icao",
+          "key": "icao"
+        },
+        {
+          "type": "string",
+          "name": "faa",
+          "key": "faa"
+        },
         {
           "type": "string",
           "name": "start_date",

images/tiler-imposm/config/layers/transport_points.json

@@ -36,6 +36,21 @@
           "name": "ref",
           "key": "ref"
         },
+        {
+          "type": "string",
+          "name": "iata",
+          "key": "iata"
+        },
+        {
+          "type": "string",
+          "name": "icao",
+          "key": "icao"
+        },
+        {
+          "type": "string",
+          "name": "faa",
+          "key": "faa"
+        },
         {
           "type": "mapping_key",
           "name": "class",