Introduce wisiwig welcome page editor
This should allow to:
- Choose the content/software to put on Kiwix Hotspot
- Customize the way how the welcome page looks like ** colors ** font ** how the content are categorized/sorted ** The visitor mode should be a readonly version of the editor more (or should we allow to customize the front page?)
All of this should be reusable for the kiwix-serve welcome page.