Modules installer

This is a simple modules installer (can't handle multiple files, or requirements yet)

It connects to http://jaspermoduleshub.herokuapp.com/

I added a `walk_packages` on `brain.py` so that modules can be installed in subfolders.
Let's rename this to `_download` to make clear that this one is the general function that calls the two special ones (`_download_git`, `_download_single_file`)