function getLaunchStoryboardImagesDir (projectRoot, platformProjDir) {
    let launchStoryboardImagesDir;
    const xcassetsExists = folderExists(path.join(projectRoot, platformProjDir, 'Assets.xcassets'));

    if (xcassetsExists) {
        launchStoryboardImagesDir = path.join(platformProjDir, 'Assets.xcassets', 'LaunchStoryboard.imageset');
    } else {
        // if we don't have a asset library for images, we can't do the storyboard.
        launchStoryboardImagesDir = null;
    }

    return launchStoryboardImagesDir;
}
Returns the directory for the Launch Storyboard image set, if image sets are being used. If they aren't
being used, returns null.

@param  {string} projectRoot        The project's root directory
@param  {string} platformProjDir    The platform's project directory