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/codegen.json

@@ -0,0 +1,28 @@
+{
+  "schema": {
+    "http://localhost:3001/shop-api": {}
+  },
+  "documents": [
+    {
+      "./framework/vendure/**/*.{ts,tsx}": {
+        "noRequire": true
+      }
+    }
+  ],
+  "generates": {
+    "./framework/vendure/schema.d.ts": {
+      "plugins": ["typescript", "typescript-operations"],
+      "config": {
+        "scalars": {
+          "ID": "string"
+        }
+      }
+    },
+    "./framework/vendure/schema.graphql": {
+      "plugins": ["schema-ast"]
+    }
+  },
+  "hooks": {
+    "afterAllFileWrite": ["prettier --write"]
+  }
+}