Add an experimental high contrast color theme to SCM-Manager. The high contrast mode uses a dark background and color with a high contrast for a better accessibility.
The change adds the theme to ui-styles and theme switcher to the storybook of ui-components.
The styleguide for usage of visual elements has not been updated for a long time. In the course of this story it should be adapted to the current standards and rules. In addition, heavy violations were rectified directly.
