Responsive layout

We should develop the frontend pages to look good on a mobile sized screen. This is best done by activating developer tools in the browser and using the device toolbar to select a mobile framing. This should ensure that the app looks good from mobile up. However to ensure it looks good on much larger screens we'll contain the content up to the Material-UI md breakpoint by adding the following to frontend/src/App.tsx,

import Container from "@material-ui/core/Container";
...

const App = () => {
  ...
  return (
    ...
      <Container maxWidth="md">
        <Router />
      </Container>
  );
};