calls a user-defined handler for each listed option of a parentId
| parentId | string|number | id of a select button | 
| handler | function | a user-defined function, the id of a listed option will be passed as an argument | 
myToolbar.forEachListOption(parentId, function(optionId){
    // your code here
});
// or
function doWithListOption(optionId){
    // your code here
}
myToolbar.forEachListOption(parentId, doWithListOption);