add submodule and paver task to build Java4Python

This integrates Java4Python as a submodule and adds the paver task `java4python` (fixes #144).

This should probably be merged after the pull request to the Java4Python repo.

This also adds a project-specific pavement file to every course. This allows you to run `paver build` from any course directory and build the text.

I updated the main `pavement.py` to just delegate to the individual pavements.