Address maintainability issues (technical debt)

[nicholaschiang]

I should address the maintainability issues (i.e. technical debt) brought up by CodeClimate:

• Create a reusable API request method checker, so that I can use:

  if (isValidMethod('GET', req.method, res)) // do stuff

Instead of:

  if (req.method !== 'GET') {
    res.setHeader('Allow', ['GET']);
    res.status(405).end(`Method ${req.method as string} Not Allowed`);
  } else {
    // do stuff
  }

• Refactor the isModelJSON() methods to throw errors instead of return.
• Create a reusable useNProgress(isLoading: boolean) hook so I can use:

  useNProgress(loading, setError);

Instead of:

  useEffect(() => {
    if (!loading) {
      NProgress.done();
    } else {
      NProgress.start();
      setError('');
    }
  }, [loading]);

• Refactor for "cognitive complexity" (various functions).