Apply Gabor's feedback.

- Install in aquilon.protocols namespace.
- Install the protobuf files, to allow compilation into other
  languages.
Use properties to choose the installation path of Python modules.

I haven't found a way to tell maven to use %python_sitelib as the
install path for the modules.  So, instead of that, we use
properties, and we may redefine the install path for the RPM from the
command line.
Add a gitignore.