Add park labels layer

layers/park_label/README.md

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+## park_label
+
+### Docs
+Read the layer documentation at **http://openmaptiles.org/schema#park_label**
+
+### Mapping Diagram
+![Mapping diagram for park](mapping_diagram.png?raw=true)
+
+### ETL diagram
+![ETL diagram for park](etl_diagram.png?raw=true)

layers/park_label/layer.sql

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+-- etldoc: layer_park_label[shape=record fillcolor=lightpink, style="rounded,filled",
+-- etldoc:     label="layer_park |<z6> z6 |<z7> z7 |<z8> z8 |<z9> z9 |<z10> z10 |<z11> z11 |<z12> z12|<z13> z13|<z14> z14+" ] ;
+
+CREATE OR REPLACE FUNCTION layer_park_label(bbox geometry, zoom_level int, pixel_width numeric)
+RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text, name_de text, tags hstore, class text, rank int) AS $$
+    SELECT osm_id, geometry_point, name, name_en, name_de, tags,
+        COALESCE(NULLIF(boundary, ''), NULLIF(leisure, '')) AS class,
+        row_number() OVER (
+           PARTITION BY LabelGrid(geometry_point, 100 * pixel_width)
+           ORDER BY
+               (CASE WHEN boundary = 'national_park' THEN true ELSE false END) DESC,
+               (COALESCE(NULLIF(tags->'wikipedia', ''), NULLIF(tags->'wikidata', '')) IS NOT NULL) DESC,
+               area DESC
+        )::int AS "rank"
+        FROM (
+        -- etldoc: osm_park_polygon_gen8 -> layer_park_label:z6
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen8
+        WHERE zoom_level = 6
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen7 -> layer_park_label:z7
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen7
+        WHERE zoom_level = 7
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen6 -> layer_park_label:z8
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen6
+        WHERE zoom_level = 8
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen5 -> layer_park_label:z9
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen5
+        WHERE zoom_level = 9
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen4 -> layer_park_label:z10
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen4
+        WHERE zoom_level = 10
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen3 -> layer_park_label:z11
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen3
+        WHERE zoom_level = 11
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen2 -> layer_park_label:z12
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen2
+        WHERE zoom_level = 12
+        UNION ALL
+
+        -- etldoc: osm_park_polygon_gen1 -> layer_park_label:z13
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon_gen1
+        WHERE zoom_level = 13
+        UNION ALL
+
+        -- etldoc: osm_park_polygon -> layer_park_label:z14
+        SELECT osm_id, geometry_point, name, name_en, name_de, tags, leisure, boundary, area
+        FROM osm_park_polygon
+        WHERE zoom_level >= 14
+    ) AS zoom_levels
+    WHERE geometry_point && bbox;
+$$ LANGUAGE SQL IMMUTABLE;

layers/park_label/park_label.yaml

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+layer:
+  id: "park_label"
+  description: |
+      Labels for `park` layer.
+  buffer_size: 64
+  fields:
+    name: The OSM [`name`](http://wiki.openstreetmap.org/wiki/Key:name) value of the peak.
+    name_en: English name `name:en` if available, otherwise `name`.
+    name_de: German name `name:de` if available, otherwise `name` or `name:en`.
+    class:
+      description: |
+          Use the **class** to differentiate between different parks.
+      values:
+      - national_park
+      - nature_reserve
+    rank: Rank of the park within one tile (starting at 1 that is the most important park).
+  datasource:
+    geometry_field: geometry
+    query: (SELECT geometry, class, name, name_en, name_de, {name_languages}, rank FROM layer_park_label(!bbox!, z(!scale_denominator!), !pixel_width!)) AS t
+schema:
+  - ./layer.sql
+datasources:
+  - type: imposm3
+    mapping_file: ../park/mapping.yaml