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/.babelrc.js

@@ -7,6 +7,6 @@ if (process.env.NODE_ENV !== `test`) {
 }
 
 module.exports = {
-  presets: [["babel-preset-medusa-package"]],
+  presets: [["babel-preset-medusa-package"], ["@babel/preset-typescript"]],
   ignore,
 }