Package the protocol buffers part

I retry here the packaging patches, since sending them to the mailing list failed.

The packaging is done with Maven, as usual. Compiling the protocol buffers part with a setup.py and packaging that is awfully complicated. And I know how to do it with Maven.

Notes:

* Python files are installed in `/usr/lib/python<python.version>/site_packages/aquilon/protocols`, where `python.versìon` defaults to 2.6 and can be overridden in the command line with `-Dpython.version=X.Y`.
* This means Python files belong in the `aquilon.protocols` namespace, as suggested in previous feedback.  Does this match the imports in Aquilon?
. Does Aquilon behave this way?
* Protocol buffers and generated CPP files are installed under `/usr/share/aquilon/protocols`.