Adds plugin for Contentful synchronization (#75)

Adds plugin for Contentful

Will create product and product variants in Contentful, when created in Medusa

Closes #47

packages/medusa/src/models/product-variant.js

@@ -13,6 +13,8 @@ class ProductVariantModel extends BaseModel {
   static schema = {
     title: { type: String, required: true },
     prices: { type: [MoneyAmountSchema], default: [], required: true },
+    sku: { type: String, default: "" },
+    barcode: { type: String, default: "" },
     options: { type: [OptionValueSchema], default: [] },
     image: { type: String, default: "" },
     published: { type: Boolean, default: false },