Since this handles arbitrary paths, we get an error on `favicon.icoCommand` :-). I think this factory business is over-complicated, but you should at least be white-listing them or something.

```
    return run_command(command, request, None)
  File "/home/tavish/capstone/nbdiff/nbdiff/server/remote_server.py", line 33, in run_command
    command = get_class(cmd).newInstance()
  File "/home/tavish/capstone/nbdiff/nbdiff/server/remote_server.py", line 25, in get_class
    obj = __import__(module)
ImportError: No module named favicon.icoCommand
```