CLC-4259 - Allow instructors to download their final grades

https://jira.ets.berkeley.edu/jira/browse/CLC-4259
@redconfetti Do we need to put this in an array? Does it work without it as well?

```javascript
var url = '/courses/' + course_id + '/gradebook';
if (url.indexOf(window.location.pathname) !== -1) {
```