Fix and improve colors

1. Set correct warn color for light theme
2. Use color with better contrast for snackbar text
3. Improve color palettes
Improve colors for green, red, yellow and blue and make them consistent. For dark theme use same colors as in light theme with less saturation.

Introduce new variables for icon colors on imverted backgrounds as in snackbar.

Also introduce --success variables to use them instead of --green for success indicators.

4. Use correct colors for success and warn indicators
Instead of using --green and --red use --success and --warn colors.

5. Fix dark theme color for menu divider

Closes #1157 (closed), #1163 (closed), #1164 (closed)