Always show columns headers

Fixes #579

Signed-off-by: Ryan O'Hara <oharar@email.chop.edu>
Can this all be moved into onRender and replace the `$('.navbar-fixed-top')` reference with `this.ui.navbarTop` while also adding:

```javascript
ui: {
    navbarTop: '.navbar-fixed-top'
},
```

below the `itemView: row.Row` line?