Generate certificates, use a password

It bothers me to set people up with this docker container and not use an encrypted connection by default. This establishes a certificate at runtime and accepts a password:

```
docker run -p 8888:8888 -e PASSWORD=GreatPassword ipython/notebook
```

With some modification, this could accept a user's certificate too.

We'll have to (want to?) handle https://github.com/tornadoweb/tornado/issues/523 directly though to let HTTP redirect to HTTPS. Would packaging nginx+conf in here make sense?