Add topbar to page and refactor existing code

frontend/src/components/App.scss

frontend/src/components/App.tsx

frontend/src/components/molecules/Buttons.tsx

frontend/src/components/molecules/Toasts.tsx

frontend/src/components/organisms/Buttonbar.tsx

frontend/src/components/organisms/Toastbar.tsx

frontend/src/components/organisms/TopBar/TopBar.tsx

frontend/src/components/organisms/TopBar/style.scss

frontend/src/components/pages/ExamplePage.tsx

frontend/src/components/pages/Scientia.tsx

frontend/src/images/logo.svg

frontend/src/images/user.png

frontend/src/index.tsx

frontend/src/scss/custom.scss