WIP: Use Custom 404 And 500 Templates

[dchukhin]

ClickUp ticket: https://app.clickup.com/t/8684yagqm

As noted in the ClickUp ticket, the site is currently not defining a template to use for 404 (or a 500) status code responses. As a result, the page for such responses looks not great.

It turns out the code actually has functions for handling 404 and 500 status-code responses, but they weren't hooked up as Django expected, and the templates (404.html and 500.html) didn't exist.
This pull request:

• hooks up the handlers for 404 and 500 status-code responses as expected by Django
• adds the necessary HTML templates (404.html and 500.html)

To test locally:

• set the following in your local.py settings file:

DEBUG=False
STATICFILES_STORAGE = "django.contrib.staticfiles.storage.StaticFilesStorage"

To see the 404 page:

• visit a URL that doesn't exist
  To see the 500 page:
• add some code that causes an error
  • for example, in apps/hip/views.py, just below the def handler404(request, *args, **argv): line, add something like 1/0, then visit a URL that doesn't exist

TODO:

• make the templates look better
• remove things from the 500.html template that could themselves cause a 500 error