Java fixes, tests and examples for ALS, KMeans

This change addresses some of the issues with using MLLib from Java programs. Specifically it fixes the `train` interface to not use Ints or Doubles and also renames methods to make them easier to call. 

As a way to check if the Java interface works, we have two additions: a. A set of Java examples in the `examples` project that read a data file and run the algorithms. b. A set of unit tests which check if the basic methods can be called and work as expected.