Use classnames package for scss classes

[namsnath]

classnames is a simpler way to interact with class names in React.

Allows for using an array or dict to defined classes, can make code a lot cleaner.

/* components/submit-button.js */
import { Component } from 'react';
import classNames from 'classnames/bind';
import styles from './submit-button.css';

let cx = classNames.bind(styles);

export default class SubmitButton extends Component {
  render () {
    let text = this.props.store.submissionInProgress ? 'Processing...' : 'Submit';
    let className = cx({
      base: true,
      inProgress: this.props.store.submissionInProgress,
      error: this.props.store.errorOccurred,
      disabled: this.props.form.valid,
    });
    return <button className={className}>{text}</button>;
  }
};