Major responsive design update

[JanProgrammierung]

• Added Tailwind classes to several pages to make them more mobile friendly
• Changed the header, made it broader (temporary), updated links, added SVG for mobile view
• Deleted unused pages and code. (Not commented out because it's unlikely the code will be reused. If it will be reused, we can always go back in the GitHub branch history)
• Took out the Body classes for now to make the mobile design friendlier. Trying to add a different set of Body classes before the conference in a different way to make the page "slim" again. Some pages have minimal padding/margin to the left and right end of the screen now, this will be fixed asap.