Added script to create data_units table

\approve @fd

migrations/00004_create-table-data-units.sql

+CREATE TABLE public.data_units
+(
+    data_unit_id VARCHAR,
+    occupancy_case occupancycase,
+    aggregated_source_id SMALLINT,
+    exposure_entity CHAR(3),
+    buildings_total FLOAT,
+    dwellings_total FLOAT,
+    people_census FLOAT,
+    cost_total FLOAT,
+
+    PRIMARY KEY (data_unit_id, occupancy_case, aggregated_source_id)
+
+);
+
+ALTER TABLE public.data_units
+OWNER TO postgres;