Replace default.html with a regular view

[jhass]

So we can correctly reference the images, fixes #5280

This is solely to close #5280, it explicitly does not:

• cleanup the CSS
• update the content
• make the content translatable
• change the design so it integrates well into the rest of the application

These are all tasks that should be done in the mid-term, but not here.

[denschub]

Thank you very much!

[Flaburgan]

I think I should be able to work on this later in the spring.