new system to load backends

Now there is a single file ~/.weboob/backends, where every backends are
instancied. There are two ways to create backends for frontends:
- Use Weboob.load_backends(), to load every backends in the config file
- Use Weboob.load_modules(), to instanciate every module one time

weboob/backends/canaltp/backend.py

@@ -24,6 +24,7 @@ from weboob.capabilities.travel import ICapTravel, Station, Departure
 from .browser import CanalTP
 
 class CanalTPBackend(Backend, ICapTravel):
+    NAME = 'canaltp'
     MAINTAINER = 'Romain Bignon'
     EMAIL = 'romain@peerfuse.org'
     VERSION = '1.0'