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 ?
Do we really need to set the description and the status at the instantiation? I think it can be statically set in the constructor since it's a property of the module, we don't want to change it without a code modification