refactoring of account settings into multiple screens

src/widgets/button-back.jsx

@@ -0,0 +1,12 @@
+// The <- button to be displayed in title bars.
+import React from 'react';
+
+export default class ButtonBack extends React.PureComponent {
+  render() {
+    return (
+      <a href="#" onClick={(e) => {e.preventDefault(); this.props.onBack();}}>
+        <i className="material-icons">arrow_back</i>
+      </a>
+    );
+  }
+}