ext: Add library updaters to extensionss

mopidy/backends/local/__init__.py

@@ -29,3 +29,7 @@ class Extension(ext.Extension):
     def get_backend_classes(self):
         from .actor import LocalBackend
         return [LocalBackend]
+
+    def get_library_updaters(self):
+        from .library import LocalLibraryUpdateProvider
+        return [LocalLibraryUpdateProvider]

mopidy/ext.py

@@ -79,6 +79,9 @@ class Extension(object):
         """
         return []
 
+    def get_library_updaters(self):
+        return []
+
     def register_gstreamer_elements(self):
         """Hook for registering custom GStreamer elements