Add OAuth2 authentication (#147)

- Added Site settings > Authentication section
- Create/edit/delete your custom oauth2 configurations
- Login or signup with oauth2

app/javascript/components/SiteSettings/Authentication/index.tsx

@@ -0,0 +1,33 @@
+import * as React from 'react';
+import { Provider } from 'react-redux';
+import { Store } from 'redux';
+
+import AuthenticationSiteSettings from '../../../containers/AuthenticationSiteSettings';
+import createStoreHelper from '../../../helpers/createStore';
+import { State } from '../../../reducers/rootReducer';
+
+interface Props {
+  authenticityToken: string;
+}
+
+class AuthenticationSiteSettingsRoot extends React.Component<Props> {
+  store: Store<State, any>;
+
+  constructor(props: Props) {
+    super(props);
+
+    this.store = createStoreHelper();
+  }
+
+  render() {
+    return (
+      <Provider store={this.store}>
+        <AuthenticationSiteSettings
+          authenticityToken={this.props.authenticityToken}
+        />
+      </Provider>
+    );
+  }
+}
+
+export default AuthenticationSiteSettingsRoot;