Reapply "feat(loyalty): EnakPoint & EnakCoin" (#32)

This reverts commit 4e24f9bbb0.

migrations/000094_add_point_payment_method.down.sql

@@ -0,0 +1,16 @@
+ALTER TABLE payments
+    DROP CONSTRAINT IF EXISTS chk_payments_point_pair,
+    DROP COLUMN IF EXISTS point_value,
+    DROP COLUMN IF EXISTS points_used;
+
+DROP TRIGGER IF EXISTS trigger_create_point_payment_method ON organizations;
+DROP FUNCTION IF EXISTS create_point_payment_method();
+
+-- Fails if an EnakPoint method has been used by a payment, which is the point: those
+-- payments would lose their method.
+DELETE FROM payment_methods WHERE type = 'point';
+DROP INDEX IF EXISTS uq_payment_methods_point_per_organization;
+
+ALTER TABLE payment_methods DROP CONSTRAINT IF EXISTS payment_methods_type_check;
+ALTER TABLE payment_methods ADD CONSTRAINT payment_methods_type_check
+    CHECK (type IN ('cash', 'card', 'digital_wallet'));