react-native example app port (#223)

* add readme

* react-native example app

* update readme

* add ios-cli dep

* revert package.json change

* update readme

* update readme

* don't auto launch metro

* add react native scripts

* nohoist @react-native-community/**

* update readme

* undo wrong README change

* remove react-native root dep

* copyright headers

* semi-style

* add default gitignore

* finish linting

* remove test for now

* fix typescript errors

* fix linting

* update scripts

* update deps and version

* update readme

* remove accidental dep

* update readme

* bump deps

* update yarn.lock

* actually update yarn.lock

* fix yarn.lock conflicts by updating exampleReactNative deps

packages/exampleReactNative/nodeGlobalsShim.js

@@ -0,0 +1,45 @@
+// Copyright 2017-2019 @polkadot/example-react authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+/* eslint-disable no-global-assign */
+
+import AsyncStorage from '@react-native-community/async-storage';
+
+class Storage {
+  constructor () {
+    this.dataMap = new Map();
+    this.loading = true;
+  }
+
+  init = async () => {
+    const keys = await AsyncStorage.getAllKeys();
+    const data = await AsyncStorage.multiGet(keys);
+    data.forEach(this.saveItem.bind(this));
+    this.loading = false;
+    return [...data];
+  }
+
+  getItem = key => {
+    return this.dataMap.get(key);
+  }
+
+  setItem = (key, value) => {
+    this.dataMap.set(key, value);
+    return AsyncStorage.setItem(key, value);
+  }
+
+  remove = key => {
+    this.dataMap.delete(key);
+    return AsyncStorage.removeItem(key);
+  }
+
+  saveItem = item => {
+    this.dataMap.set(item[0], item[1]);
+  }
+}
+
+// Set global process variable expected by some classes.
+global.process = require('process');
+global.navigator.userAgent = '';
+window = { location: { host: '' } };
+global.localStorage = new Storage();