Add HTML page titles with i18n

```javascript
import React from 'react'
import Helmet from 'react-helmet'
import PropTypes from 'prop-types'

import { generalConfig } from '../config'

const PageTitle = ({ title }) => (
  <Helmet>
    <title>{title}</title>
  </Helmet>
)

PageTitle.propTypes = {
  title: PropTypes.string
}

PageTitle.defaultProps = {
  title: generalConfig.title
}

```