Fix backup plugin

Update required Python version
Update pyln and other packages
Update README

backup/backends.py

@@ -0,0 +1,33 @@
+'''Create a backend instance based on URI scheme dispatch.'''
+from typing import Type
+from urllib.parse import urlparse
+
+from backend import Backend
+from socketbackend import SocketBackend
+from filebackend import FileBackend
+
+
+def resolve_backend_class(backend_url):
+
+    backend_map: Mapping[str, Type[Backend]] = {
+        'file': FileBackend,
+        'socket': SocketBackend,
+    }
+    p = urlparse(backend_url)
+    backend_cl = backend_map.get(p.scheme, None)
+    return backend_cl
+
+
+def get_backend(destination, create=False, require_init=False):
+    backend_cl = resolve_backend_class(destination)
+    if backend_cl is None:
+        raise ValueError("No backend implementation found for {destination}".format(
+            destination=destination,
+        ))
+    backend = backend_cl(destination, create=create)
+    initialized = backend.initialize()
+    if require_init and not initialized:
+        kill("Could not initialize the backup {}, please use 'backup-cli' to initialize the backup first.".format(destination))
+    assert backend.version is not None
+    assert backend.prev_version is not None
+    return backend