Add convenient wrapper for confirm and alert about tingle

[juanvillegas]

We implemented a wrapper around your library to display messages in our app (rocketlanguages.com). And needed "sugar" for confirm and alert. We solved this using Promises, which resulted pretty well. In case anyone is interested, here is a simplified example (our wrapper has some more use-case specific stuff):

• We created a window.RocketMessages namespace and added confirm() and alert() to it
• Calling confirm() creates a tingle modal with some defaults and returns an ES6 promise, like so:

return new Promise((resolve, reject) => {
    tingleModalObject.addFooterBtn("Ok button", "your class", () => { resolve(true); });
    tingleModalObject.addFooterBtn("Cancel button", "your class", () => { resolve(false); });
});

• In your client code, you can use it like:

window.RocketMessages.confirm("Confirm delete?").then((userResponse) => {
    if (userResponse) {
       // user clicked "ok"
    } else {
       // user clicked "cancel"
    }
});

Good work by the way!
Cheers!