saveSettings = (settings) => {
  PropertiesService.getScriptProperties().setProperty('calendar', JSON.stringify(settings.calendarSettings));
  PropertiesService.getScriptProperties().setProperty('syncFrom', settings.syncFrom);
  PropertiesService.getScriptProperties().setProperty('syncTo', settings.syncTo);
  PropertiesService.getScriptProperties().setProperty('isUpdateTitle', settings.isUpdateCalendarItemTitle);
  PropertiesService.getScriptProperties().setProperty('isUseCategoriesAsCalendarItemTitle', settings.isUseCategoriesAsCalendarItemTitle);
  PropertiesService.getScriptProperties().setProperty('isUpdateDescription', settings.isUpdateCalendarItemDescription);
  return 'Settings saved';
}
Saves the settings from the sidebar