Scala/Spark-Bindings documentation

[Sebastian Schelter]

I wonder whether we should have an extra toplevel navigation point for 
the Scala/Spark-Bindings documentation. Currently, its somehow hidden 
unter "Basic" and I think it deserves a more prominent place. We should 
also add more pages, I intend to add a quickstart page for playing with 
Mahout's spark-shell, for example.

--sebastian