Changed shell behaviour

Usage: `python manage.py shell -e dev` default `flask-script` behaviour `python shell --no-ipython` isn't possible because there is no way to pass flags.

One way to replicate this behaviour is to write `class PatchedShell` and check for `--no-ipython` and `--no-bpython` in `sys.argv` in `run`, is that ok or use argparse ?