feat(medusa): cart context (#201)

- Adds a context field to Cart
- context is automatically populated with ip + user agent
- context can be updated via POST /store/cart/:id or set when creating via POST /store/cart

integration-tests/helpers/test-server.js

@@ -1,12 +1,14 @@
 const path = require("path");
 const express = require("express");
 const getPort = require("get-port");
-
-const loaders = require("@medusajs/medusa/dist/loaders").default;
+const importFrom = require("import-from");
 
 const initialize = async () => {
   const app = express();
 
+  const loaders = importFrom(process.cwd(), "@medusajs/medusa/dist/loaders")
+    .default;
+
   const { dbConnection } = await loaders({
     directory: path.resolve(process.cwd()),
     expressApp: app,