Vendure provider (#223)

* Minimal list/detail views working with Vendure

* Implement useCart/useAddItem

* Implement useUpdateItem & useRemoveItem

* Implement useSearch

* Add operations codegen, tidy up

* Dummy checkout page

* Implement auth/customer hooks

* Use env var for Shop API url

* Add some documentation

* Improve error handling

* Optimize preview image size

* Fix accidental change

* Update Vendure provider to latest changes

* Vendure provider: split out gql operations, remove unused files

* Update Vendure provider readme

* Add local next.config to Vendure provider, update docs

* Update to use demo server

* Fix build errors

* Use proxy for vendure api

* Simplify instructions in Vendure readme

* Refactor Vendure checkout api handler

* Improve image quality

framework/vendure/lib/fragments/cart-fragment.ts

@@ -0,0 +1,42 @@
+export const cartFragment = /* GraphQL */ `
+  fragment Cart on Order {
+    id
+    code
+    createdAt
+    totalQuantity
+    subTotal
+    subTotalWithTax
+    total
+    totalWithTax
+    currencyCode
+    customer {
+      id
+    }
+    lines {
+      id
+      quantity
+      linePriceWithTax
+      discountedLinePriceWithTax
+      featuredAsset {
+        id
+        preview
+      }
+      discounts {
+        description
+        amount
+      }
+      productVariant {
+        id
+        name
+        sku
+        price
+        priceWithTax
+        stockLevel
+        product {
+          slug
+        }
+        productId
+      }
+    }
+  }
+`

framework/vendure/lib/fragments/search-result-fragment.ts

@@ -0,0 +1,24 @@
+export const searchResultFragment = /* GraphQL */ `
+  fragment SearchResult on SearchResult {
+    productId
+    productName
+    description
+    description
+    slug
+    sku
+    currencyCode
+    productAsset {
+      id
+      preview
+    }
+    priceWithTax {
+      ... on SinglePrice {
+        value
+      }
+      ... on PriceRange {
+        min
+        max
+      }
+    }
+  }
+`