Review: Offer the transcript of the demo video in an accessible manner
Closes #166 (closed)
This is building on and fixing branch 166-fix. Branch 166-fix does not need to be merged, all changes are in this branch aswell.
Having the introduction page as a dialog caused problems, because the tabindices overlapped with the underlying home page, which led to having to double click 1, 2, 3 to navigate to the respective section on the introduction page instead of selection the element on the homepage.
Opening the dialog now hides the underlying homepage and allows to navigate with a single click of 1,2,3 inside the dialog.