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.
Does this really have to be wrapped in a custom function? I'd combine `_module_exists` and `_get_module_metadata` into one function that either returns metadata or `None` (alternative: raises an error that'll be catched by `install`).