Rollout_ui introduces unneeded asset paths to the rails app that uses it

While using rollout_ui I noticed that assets directories from the engine are being referenced in the rails app that uses this gem

```
1.9.3p362 :004 > Rails.application.assets.paths.grep(/rollout_ui/).count
 => 6 
```

The reason I started to worry about this is because it looks like each additional path in the asset pipeline slows down the compilations of assets (see https://github.com/chriseppstein/compass/issues/516) due to sprockets usage of hike gem. I was looking for a way to decrease number of asset paths and noticed that a bunch came from rollout-ui. 

I refactored the gem a little to exclude assets paths. I did some other refactoring to decrease maintenance of the gem using jeweler - not sure how you feel about that so feel free to not accept that part. But it would be great to eliminate the extra asset paths