Replaces MongoDB support with PostgreSQL (#151)

- All schemas have been rewritten to a relational model
- All services have been rewritten to accommodate the new data model
- Adds idempotency keys to core endpoints allowing you to retry requests with no additional side effects
- Adds staged jobs to avoid putting jobs in the queue when transactions abort
- Adds atomic transactions to all methods with access to the data layer

Co-authored-by: Oliver Windall Juhl <oliver@mrbltech.com>

packages/medusa-test-utils/src/mock-manager.js

@@ -0,0 +1,13 @@
+export default {
+  getCustomRepository: function (repo) {
+    return repo;
+  },
+
+  transaction: function (isolationOrCb, cb) {
+    if (typeof isolationOrCb === "string") {
+      return cb(this);
+    } else {
+      return isolationOrCb(this);
+    }
+  },
+};