More consistent loading of the test fixtures (#1506)

Remove db setup from the Haskell test suite and include it in the test bash scripts.

test/fixtures/load.sql

@@ -0,0 +1,11 @@
+-- Loads all fixtures for the PostgREST tests
+
+\set ON_ERROR_STOP on
+
+\ir database.sql
+\ir roles.sql
+\ir schema.sql
+\ir jwt.sql
+\ir jsonschema.sql
+\ir privileges.sql
+\ir data.sql