Replace osmborder with imposm/SQL (#1213)

Fixes #1156
Fixes #810
Fixes #1228

This PR replaces `osmborder`, which is no longer maintained, with `imposm` mappings and SQL code to generate borders.  Key features that were moved into the imposm/SQL layer:
1. Grouping by `osm_id` and aggregating by lowest `admin_level` value so that there's only one copy of ways that are members of multiple relations.
2. Filtering out of point features in boundary relations (typically `admin_centre` and `label` roles).
3. Move disputed boundary detection logic into SQL.

This will increase the database size slightly because of the limits of what imposm can do, as some of the filtering is done in the SQL layer after importing, rather than being done in `osmborder`.

layers/boundary/boundary_name.sql

@@ -1,23 +1,25 @@
 DROP TABLE IF EXISTS osm_border_linestring_adm CASCADE;
 
 -- etldoc: osm_border_linestring -> osm_border_linestring_adm
+-- etldoc: osm_border_disp_linestring -> osm_border_linestring_adm
+-- etldoc: ne_10m_admin_0_countries -> osm_border_linestring_adm
 CREATE TABLE IF NOT EXISTS osm_border_linestring_adm AS ( 
   WITH 
     -- Prepare lines from osm to be merged
 	multiline AS (
-    	SELECT ST_Node(ST_Collect(geometry)) AS geometry, 
-			   maritime,
-			   disputed
+        SELECT osm_id,
+               ST_Node(ST_Collect(geometry)) AS geometry,
+               BOOL_OR(maritime) AS maritime,
+               FALSE AS disputed
     	FROM osm_border_linestring
-    	WHERE admin_level = 2
+    	WHERE admin_level = 2 AND ST_Dimension(geometry) = 1
 		    AND osm_id NOT IN (SELECT DISTINCT osm_id FROM osm_border_disp_linestring)
-		GROUP BY maritime,
-				 disputed
+              GROUP BY osm_id
 		),
 
 	mergedline AS (
-		SELECT (ST_Dump(
-      		     ST_LineMerge(geometry))).geom AS geometry,
+		SELECT osm_id,
+      		     (ST_Dump(ST_LineMerge(geometry))).geom AS geometry,
 			maritime,
 			disputed
   		FROM multiline
@@ -32,7 +34,7 @@ CREATE TABLE IF NOT EXISTS osm_border_linestring_adm AS (
   			FROM (SELECT ST_Node(
                           ST_Collect(geometry)) AS geometry
     			FROM osm_border_linestring
-    			WHERE admin_level = 2
+    			WHERE admin_level = 2 AND ST_Dimension(geometry) = 1
                 ) nodes
 			) linemerge
   		), 
@@ -55,12 +57,14 @@ CREATE TABLE IF NOT EXISTS osm_border_linestring_adm AS (
 	),
 
 	rights AS (
-    	SELECT adm0_r,
+        SELECT osm_id,
+			   adm0_r,
 			   geometry,
 			   maritime,
 			   disputed
 		FROM (
-			SELECT b.adm0_a3 AS adm0_r,
+			SELECT a.osm_id AS osm_id,
+                   b.adm0_a3 AS adm0_r,
                    a.geometry,
                    a.maritime,
                    a.disputed
@@ -73,14 +77,16 @@ CREATE TABLE IF NOT EXISTS osm_border_linestring_adm AS (
             ) line_rights
 		)
 
-  SELECT adm0_l,
+  SELECT osm_id,
+		 adm0_l,
 		 adm0_r,
 		 geometry,
 		 maritime,
 		 2::integer AS admin_level,
 		 disputed
   FROM (
-    SELECT b.adm0_a3 AS adm0_l,
+    SELECT r.osm_id AS osm_id,
+           b.adm0_a3 AS adm0_l,
            r.adm0_r AS adm0_r,
            r.geometry,
            r.maritime,
@@ -96,4 +102,4 @@ CREATE TABLE IF NOT EXISTS osm_border_linestring_adm AS (
 
 CREATE INDEX IF NOT EXISTS osm_border_linestring_adm_geom_idx
   ON osm_border_linestring_adm
-  USING GIST (geometry);
+  USING GIST (geometry);