setBackgroundCommand ({ slug, thang }) {
    return this.moveLankCommand({
      key: BACKGROUND,
      resource: slug,
      thang,
      ms: 0
    })
  }
Sets the background.
Handles backgrounds that may already exist or are simply being moved.
@param {Object} backgroundInfo
@param {string} backgroundInfo.slug Background object slug
@param {Object} backgroundInfo.thang The thang object for the background. Contains scale and position information.