Basic command-line API

Adds two django management commands - add_switch and remove_switch.

A couple of times while working on apps with gargoyle, I've ended up writing a simple command to be able to add, update and remove simple switches from the command line. If it might be useful for others, it'd be better off upstream.

python manage.py add_switch foobar
python manage.py add_switch foobar --disabled
python manage.py remove_switch foobar

Thanks!