Commercial variable number of items in dfp component styling

This adds styles for variations on the DFP commercial component allowing for 2 and 3 item components to be displayed.

It uses the same template, (that will be updated when this goes live) as exists at the moment meaning we have less to look after long term.

Tested across fronts and articles and with page skins.

Before, (4 items);
![screen shot 2014-07-01 at 14 56 18](https://cloud.githubusercontent.com/assets/1303616/3443872/48ec2488-0128-11e4-8d41-3b6f5a07a84a.png)

After (3 items);
![screen shot 2014-07-01 at 15 00 43](https://cloud.githubusercontent.com/assets/1303616/3443879/5321b968-0128-11e4-9f5b-92c1e3858771.png)

After (2 items)
![screen shot 2014-07-01 at 15 00 51](https://cloud.githubusercontent.com/assets/1303616/3443883/5d60932c-0128-11e4-963b-fc095d58e1f4.png)

any reason they're nested, rather than

```
&.commercial--dfp-3 .lineitem {
....
}
```

?