Added Attract extension.

For now it just contains a management command, but I ensured it is
registered properly through the Pillar extension system.

cloud.py

@@ -1,8 +1,12 @@
 #!/usr/bin/env python
 
 from pillar import PillarServer
+from bcloud.attract.extension import AttractExtension
+
+attract = AttractExtension()
 
 app = PillarServer('.')
+app.load_extension(attract, '/attract')
 app.process_extensions()
 
 if __name__ == '__main__':