Updates to module cards to make the platform production-ready

[JaroCamphuijsen]

• [x] Hide or remove all modules without content
• [x] Remove the "upcoming" category
• [x] Add descriptions to allow for description display on module cards

Descriptions of module cards only work with the NEBULA update in https://github.com/esciencecenter-digital-skills/NEBULA/pull/61 please also use this branch of NEBULA to test locally.

[JaroCamphuijsen]

Here is a screenshot that shows the intended looks of the module descriptions: