Clarify website structure

[LukasWallrich]

Thanks to Susana and Pauline for giving this some thought - this could be a place to share them and discuss, so that we can then link it into any issues that arise and changes we make.

The key question is how the overall navigation can better align with user needs. One option are these goals/categories for FORRT projects (though there is obviously some other webpage content as well that needs to go somewhere) - another is to think about user personas and their needs.