Add experimental high contrast mode (#1845)

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.

scm-ui/ui-components/src/modals/ConfirmAlert.stories.tsx

@@ -44,7 +44,7 @@ const buttons = [
   }
 ];
 
-storiesOf("Modal|ConfirmAlert", module)
+storiesOf("Modal/ConfirmAlert", module)
   .addDecorator(story => <MemoryRouter initialEntries={["/"]}>{story()}</MemoryRouter>)
   .add("Default", () => <ConfirmAlert message={body} title={"Are you sure about that?"} buttons={buttons} />)
   .add("WithButton", () => {

scm-ui/ui-components/src/modals/Modal.stories.tsx

@@ -71,7 +71,7 @@ const withFormElementsFooter = (
   </ButtonGroup>
 );
 
-storiesOf("Modal|Modal", module)
+storiesOf("Modal/Modal", module)
   .addDecorator((story) => <MemoryRouter initialEntries={["/"]}>{story()}</MemoryRouter>)
   .add("Default", () => (
     <NonCloseableModal>