Suppress rendering of underground buildings (#1241)

This PR does the following:
1. Suppresses underground buildings from rendering, when such buildings are tagged `location=underground`.  Based on the wiki documentation, the `layer` tag does not determine whether a feature is above of below ground.
2. Unifies the building and building relation imposm exclusion mappings.

The following underground building feature in Luxembourg is used as the test object:
https://www.openstreetmap.org/way/582873794

layers/building/mapping.yaml

@@ -60,11 +60,14 @@ tables:
       aeroway:
       - terminal
       - hangar
+      location:
+      - underground
     filters:
       reject:
         building: ["no","none","No"]
         building:part: ["no","none","No"]
         man_made: ["bridge"]
+        location: ["underground"]
     type: polygon
 
   # etldoc: imposm3 -> osm_building_relation
@@ -157,4 +160,4 @@ tables:
       type: member_type
     mapping:
       type: [building]
-    type: relation_member
+    type: relation_member