Added option to disable request logging.

The JSON API server can now be started with `-q` or `--quiet` to disable the logging performed by BaseHTTPRequestHandler. This means that the terminal spawning the API server doesn't become an endlessly scrolling nightmare. It also boosts the requests handled per second by some 20%, and even more for environments with slow terminals.

Also made the `demo.py` and `api_server.py` files executable.