code: function prefix(event, properties) {
    var prefixed = {};
    each(properties, function(key, val) {
      if (key === 'Billing Amount') {
        prefixed[key] = val;
      } else {
        prefixed[event + ' - ' + key] = val;
      }
    });
    return prefixed;
  }
docs: Prefix properties with the event name.
  
  @param {String} event
  @param {Object} properties
  @return {Object} prefixed
  @api private