💄 remove themes and slightly improve design

[BuildmodeOne]

Maybe quite controversial but I have removed the Retro, Barbie, Windows95 themes.

These themes all have a bad UX and readability of texts. In addition, a few themes no longer matched the rest of the UI and will only hold us back in the further development of the app in the future if we continue to maintain them.

To compensate, I have improved the Hackerman theme and it is much more readable.

• Removed themes
  • Retro
  • Barbie
  • Windows95
• improved Hackerman theme
• changed timetable notice
• added User Button on desktop in navbar

Change	Image
Added user button to Navbar
Timetable Notice
Hackerman Theme