Added JAVA generator from Arthur Benemann

This PR adds the JAVA MAVLink generator from Arthur Benemann.

@arthurbenemann There are a couple of items I would like to check with you:

  1. Tridge and I want to re-license MAVLink as BSD (or similar), because LGPL is a bit confusing with a header only library and our intent is to be open and permissive. Are you ok to re-license all code in this PR as BSD (2 or 3 clause), MIT or Apache? Did you write all of the code or are there other authors we have to ask?

  2. I had to change your folder structure slightly, because MAVLink supports more than one dialect. It now would look like this:

![2014-08-07 07 19 16 pm](https://cloud.githubusercontent.com/assets/1208119/3845904/789dc01e-1e57-11e4-8a5f-9d42aa59f04c.png)

  3. Would you be willing to continue to work on this generator rather than maintaining your own? It would help the community to have one common standard and not three (there are three) incompatible Java generators.