Decouple module slugs from topnav text

[dirkcuys]

Currently modules are implied by the name of the folder they are in. That leads to problems with URLs or titles once the module name is more than a single word ie. "Getting Started".

To solve this, we can decouple the text used for display from the slug used for the URL for modules as done for the how to talk about race course. See the changeset for details.