Use docopts for management command

Replaces [Flask-Script](http://flask-script.readthedocs.org/en/latest/) with [docopt](https://github.com/docopt/docopt) because awesome.

```
Usage: manage.py COMMAND [-p <port>] [--debug]

Options:
    --debug     	watch for changes and reload app
	-p <port>   	use an alternate port number

Commands:
	runserver		run the Flask application
```