Towards reproducible deployment

This includes three changes made over the course of getting _tryhaskell_ ready to deploy with Halcyon.

1. Instead of hardcoding port 4001, read the `PORT` environment variable.

2. Give _mueval_ more time, as mentioned in https://github.com/chrisdone/tryhaskell/issues/21#issuecomment-61946338

3. Instead of always loading jQuery over HTTP, use the appropriate protocol.