Spark feedback

* new js library included (bootstrap 3), newer version of jquery and ui
* introduction of `org.apache.spark.ui.notebook.front.widgets.SparkInfo` that shows  a simple and evolutive summary of the Spark work. The following will poll the result every 5 seconds, indefinitely.
```{scala}
import org.apache.spark.ui.notebook.front.widgets.SparkInfo
import scala.concurrent.duration._
new SparkInfo(sparkContext, checkInterval=5 seconds, execNumber=None)
```
The above snippet will show the below feedback besides the Spark UI (count words of a wikipedia dump):
![spark-progress](https://cloud.githubusercontent.com/assets/663344/4873321/b73e624e-620c-11e4-8b1a-a96b4790e33c.gif)