async stopAll ({ state, dispatch }, opts = {}) {
      const unload = opts.unload

      const stops = Object.keys(state.tracks)
        .map(track => dispatch('stopTrack', { track, unload }))

      const ids = await Promise.all(stops)
      return ids.flat()
    }
Stops all tracks and clears current play data.  Removes all
currently playing sounds.  Calling stop resets all data on all
tracks regardless of play state for each track.

@param opts.unload {boolean} Unload sound from memory

@return Array of sound IDs that were stopped