add Google auth plugin

plugins/talk-plugin-google-auth/client/components/GoogleButton.js

@@ -0,0 +1,11 @@
+import React from 'react';
+import { BareButton } from 'plugin-api/beta/client/components/ui';
+import styles from './GoogleButton.css';
+
+export default ({ onClick, children }) => {
+  return (
+    <BareButton className={styles.button} onClick={onClick}>
+      {children}
+    </BareButton>
+  );
+};