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 ?
The list of enabled modules must be configurable with the settings.py file, something like this:
```
from jormungandr.modules.tisseo_routing.TisseoRouting import TisseoRouting
from jormungandr.modules.v1_routing.v1_routing import V1Routing
modules = {'v1': V1Routing, 'tisseo/test':  TisseoRouting}
```
then
```
for prefix, module in modules.iteritems():
    rest_api.module_loader.load(module(rest_api, prefix))
```