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/dlfp/backend.py

@@ -24,10 +24,14 @@ from weboob.capabilities.updatable import ICapUpdatable
 from feeds import ArticlesList
 
 class DLFPBackend(Backend, ICapMessages, ICapMessagesReply, ICapUpdatable):
+    NAME = 'dlfp'
     MAINTAINER = 'Romain Bignon'
     EMAIL = 'romain@peerfuse.org'
     VERSION = '1.0'
     LICENSE = 'GPLv3'
+    CONFIG = {'username': Backend.ConfigField(description='Username on website'),
+              'password': Backend.ConfigField(description='Password of account', is_masked=True)
+             }
 
     def iter_messages(self):
         articles_list = ArticlesList('newspaper')