Store and display the location of packages

Store the location a package can be found at, and display this on the package
page.

If available, link off to the git repository containing the package.

sqitch/deploy/add_location_information.sql

@@ -0,0 +1,20 @@
+-- Deploy guix-data-service:add_location_information to pg
+
+BEGIN;
+
+CREATE TABLE locations (
+    id integer GENERATED BY DEFAULT AS IDENTITY,
+    file character varying NOT NULL,
+    line integer NOT NULL,
+    column_number integer NOT NULL,
+    CONSTRAINT file_line_column PRIMARY KEY(file, line, column_number),
+    UNIQUE (id)
+);
+
+ALTER TABLE package_metadata ADD COLUMN location_id integer REFERENCES locations(id);
+
+ALTER TABLE package_metadata DROP CONSTRAINT synopsis_description_home_page;
+
+ALTER TABLE package_metadata ADD CONSTRAINT synopsis_description_home_page_location_id UNIQUE (synopsis, description, home_page, location_id);
+
+COMMIT;