Add general region table

script/sql/create/32.region.sql

@@ -0,0 +1,7 @@
+create table region
+(
+  id text primary key
+, boundary geometry not null unique
+);
+
+create index region_gist on region using gist(boundary);

script/sql/create/32.virtual_district.sql

@@ -1,9 +0,0 @@
-create table virtual_district
-(
-  id text primary key
-, center varchar(32) references _node(id) not null unique
-, boundary geometry unique
-, nodes varchar(32)[]
-);
-
-create index virtual_district_gist on virtual_district using gist(boundary);