Rearranging and Renabling Hokuyo

I forgot to work out a CLA before pull requesting to ros-java, so setting up a pull request now back to rosjava.

@adamantivm if you haven't already done, can you sign a CLA for @damonkohler as described [here](https://github.com/rosjava/rosjava_core)? Then I can merge this back into the rosjava organisation.

Basic gist of what is going on here:

* Moved hokuyo java code out into a java package so java people can make use of that.
* Renabled the android_tutorial_hokuyo package to work with the new gradle environment.