Returns an ExternalApplication object that represents an existing external application.
Example
let externalApp = fin.desktop.ExternalApp.wrap('my-uuid');
externalApp.addEventListener('connected', () => {
console.log('external app connected');
}, () => {
console.log('The registration was successful');
}, (reason, err) => {
console.log(`Error Message: ${err.message} Error Stack: ${err.stack}`);
});