Data transformation using Lodash in a more readable way
Take advantage of lodash's _() wrapper function, which wraps a value, and allows chaining of methods.

function grouper(screenshotsArray){
  return _.reduce(screenshotsArray, function(templateDevicesName, screenshot) {
    return templateDevicesName + ' + ' + screenshot.device;
  }, '');
}

var transformedData = _(templates).map('screenshots').groupBy(grouper).value();