Implement Material 3 colors

[bmesuere]

This pull request adapts the material 3 colors as described in here.

It uses the script from this script to generate all tones.

Changes

• Replace the old colors file with a new one.
• Change how we work with the bootstrap variables. Instead of reusing them in our code, we force our values to bootstrap and don't reuse them ourselves.
• Removal of the development style. This wasn't used anymore and could be re-added later on if we have proper theme support.
• The secondary color amber was replaced by pink. We don't use it a lot yet.

Advantages

• We follow the spec. This also makes sure everything has proper contrast. This was not the case in the old design.
• Greatly improved dark mode (instead of a home brewed one).
• Preparation for switching to dark mode using css variables. This will also make it possible to have additional themes.
• The variable files are a lot cleaner. The color file contains the raw color values, the theme file maps them to primary, secondary, info, etc. The theme-light and theme-dark files map them to semantic colors such as "background" or "on-background".

Screenshots

Home page

Exercise

Course

[jorg-vr]

Background color of flatpicker instances is gone

[bmesuere]

• token padding
• find better "success" color (regenerate greens?) -> used teal
• heatmap colors
• dark mode code editor
• dark mode about page
• bg color of code blocks in dark mode
• darker divider in dark mode
• find solution for brownish secondary color in dark tones -> used pink instead of amber

[bmesuere]

I will merge this so we can continue without merge conflicts on other branches. Your comments are still welcome, @chvp and @niknetniko.