atom/atom — pull request #4216 by benogle (2014-11-18 00:11:42+00:00)
Title: Use classes on atom-panels rather than location attributes

This is nicer for styling, and consistent with the `atom-workspace-axis` elements. So

```css
atom-panel.modal {
//..
}
```

Rather than

```css
atom-panel[location="modal"] {
//..
}
```