style suggestion

[royl88]

1. i think change Icons.Pause to Icons.Play when state=="Paused" looks better.
   src/ui/PlayerView.ts

      case 'Paused':
        this._bigButton.style.display = 'block'
        // change icon
        this._bigButton.innerHTML = Icons.Play
        this._spinner.style.display = 'none'
        break

2. better close rate-setting-box after changed rate
   src/ui/ControlBarView.ts

    addDisposableDomListener(this._playbackRate, 'click', () => {
      this._playbackRateSettingBox.classList.toggle('xp-setting-box-open')
    })
    this._playbackRateItems.forEach(item => {
      addDisposableDomListener(item, 'click', () => {
        this._player.playbackRate = parseFloat(item.dataset['rate'] || '1')
        // add this
        this._playbackRateSettingBox.classList.toggle('xp-setting-box-open')
      })
    })