Rank Your Music game, using Spotify API

* Rank music according to Spotify's popularity index
* Temporarily authenticate using [Implicit Grant Flow](https://developer.spotify.com/web-api/authorization-guide/#implicit_grant_flow)
* Pulls a random playlist from your account (must have >1 song)
* Rearrange tracks using [Waffler](https://github.com/zenahirsch/jquery-waffler) jQuery plugin
* Check answers, red indicates the current track is less popular than the track directly below
* Preview song by clicking music icon in upper right-hand corner of each track
Rather than having to re-fetch the element from the DOM, you can create the method before appending it and simply use that reference.

```javascript
$li = $(li);
$trackList.append($li);
tracks[i].li = $li;
```