feat(v2): headerlinks (#1074)

* feat(v2): headerlinks

* fix test

* nits

* remove tictactoe:

* headerIcon

* nits

* remove lang dropdown

* fix failing test

* search box

* algolia search

* use babel-eslint to resolve dynamic import

* nits

* favicon and title

* Update .eslintignore

v2/lib/theme/Search/index.js

@@ -0,0 +1,61 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+
+import './styles.css';
+
+class Search extends React.Component {
+  constructor() {
+    super();
+    this.state = {
+      enabled: true,
+    };
+  }
+
+  componentDidMount() {
+    const {siteConfig = {}, metadata = {}} = this.props;
+    const {version: thisVersion, language: thisLanguage} = metadata;
+    const {algolia} = siteConfig;
+
+    // https://github.com/algolia/docsearch/issues/352
+    const isClient = typeof window !== 'undefined';
+    if (isClient) {
+      import('docsearch.js').then(({default: docsearch}) => {
+        docsearch({
+          appId: algolia.appId,
+          apiKey: algolia.apiKey,
+          indexName: algolia.indexName,
+          inputSelector: '#search_input_react',
+          algoliaOptions: JSON.parse(
+            JSON.stringify(algolia.algoliaOptions)
+              .replace('VERSION', thisVersion)
+              .replace('LANGUAGE', thisLanguage),
+          ),
+        });
+      });
+    } else {
+      console.warn('Search has failed to load and now is being disabled');
+      this.setState({enabled: false});
+    }
+  }
+
+  render() {
+    const {enabled} = this.state;
+
+    return enabled ? (
+      <input
+        id="search_input_react"
+        type="search"
+        placeholder="Search docs"
+        aria-label="Search docs"
+      />
+    ) : null;
+  }
+}
+
+export default Search;