Routing modularization proposal

We aim to make Jormungandr more flexible.
This is a functional (almost) non intrusive modification which add a module system to Jormungandr.

All modules are now stored in modules directory.

A module have a namespace which is an url prefix.
That avoids route collision between modules

Navitia.io API is now a module prefixed by v1

The Jormungandr behaviour is unchanged

Future improvements
- generate dynamicaly the Jormungandr entry point http://api.navitia.io with modules information
- add some other example modules ?