add web_dashboard API (#333)

* add web_dashboard sample

* add docs

* address code review comments

* restructure web_dashboard

* set up provider and mock service

* add copyright headers, use relative imports

* add API class, add tests

* fmt

* rename services -> API, remove data library

* use new API in app

* add stream to items api

* convert from StreamBuilder to StreamProvider

* add subscription to Entry API

* rename API classes

* address comments

* Update README.md

* update README

* remove routing_demo

experimental/web_dashboard/lib/src/pages/home.dart

@@ -0,0 +1,49 @@
+// Copyright 2020, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import '../api/api.dart';
+import 'item_details.dart';
+
+class HomePage extends StatelessWidget {
+  Widget build(BuildContext context) {
+    var api = Provider.of<DashboardApi>(context);
+
+    return Scaffold(
+      body: StreamProvider<List<Item>>(
+        initialData: [],
+        create: (context) => api.items.allItemsStream(),
+        child: Consumer<List<Item>>(
+          builder: (context, items, child) {
+            return ListView.builder(
+              itemBuilder: (context, idx) {
+                return ListTile(
+                  title: Text(items[idx].name),
+                  onTap: () {
+                    _showDetails(items[idx], context);
+                  },
+                );
+              },
+              itemCount: items.length,
+            );
+          },
+        ),
+      ),
+      floatingActionButton: FloatingActionButton(
+        child: Icon(Icons.add),
+        onPressed: () {
+          api.items.insert(Item('Coffees Drank'));
+        },
+      ),
+    );
+  }
+
+  void _showDetails(Item item, BuildContext context) {
+    Navigator.of(context).push(MaterialPageRoute(builder: (context) {
+      return ItemDetailsPage(item);
+    }));
+  }
+}