Move aboriginal lands boundaries to boundary layer (#1604)

This PR adds indigenous lands to the `boundary` layer by adding new area features for these objects, along with generalization up to z4. It borrows heavily from the technical processing chain of the `park` layer.

I added new `class`, `name`, and `name:xx` attributes to the boundary layer, in order to support the new area features. Should we (or someone extending this schema) come up with new objects to place in the boundary layer in the future, `class` would support additional categories.

layers/place/place.yaml

@@ -5,6 +5,9 @@ layer:
       - ne_10m_admin_1_states_provinces
       - ne_10m_admin_0_countries
       - ne_10m_populated_places
+  requires:
+    layers:
+      - boundary
   description: |
       The place layer consists out of [countries](http://wiki.openstreetmap.org/wiki/Tag:place%3Dcountry),
       [states](http://wiki.openstreetmap.org/wiki/Tag:place%3Dstate), [cities](http://wiki.openstreetmap.org/wiki/Key:place)
@@ -28,7 +31,9 @@ layer:
           Distinguish between continents, countries, states, islands and
           places like settlements or smaller entities.
           Use **class** to separately style the different places and build
-          a text hierarchy according to their importance.
+          a text hierarchy according to their importance. For places derived 
+          from boundaries, the original value of the 
+          [`boundary`](http://wiki.openstreetmap.org/wiki/Key:boundary) tag.
       values:
       - continent
       - country
@@ -44,6 +49,7 @@ layer:
       - neighbourhood
       - isolated_dwelling
       - island
+      - aboriginal_lands
     iso_a2:
       description: |
           Two-letter country code [ISO 3166-1 alpha-2](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2). Available only for `class=country`.
@@ -75,7 +81,7 @@ schema:
   - ./types.sql
   - ./capital.sql
   - ./city.sql
-  - ./island_rank.sql
+  - ./area_rank.sql
   - ./update_continent_point.sql
   - ./update_country_point.sql
   - ./update_island_polygon.sql