feat(error-handling): custom 404 handler

- Create a custom 404 Not Found page and improve the handler404 with a better 404.html template
- Add comments, formatting, and pylint suppressions to satisfy pylint
- Apply Black formatting
- Remove unnecessary DEBUG line

Refs: #100, PR#102

web-app/django/VIM/templates/404.html

@@ -1,10 +1,15 @@
 {% extends "base.html" %}
-
-{% block title %}
-Oops
-{% endblock %}
-
 {% block content %}
-<h1>Oops</h1>
-<h2>We can't seem to find the page you are looking for.</h2>
-{% endblock%}
+<div class="container">
+    <div class="row">
+        <div class="p-3 col-12">
+            <h3>404</h3>
+            <h5>Page not found</h5>
+            <br>
+            <p>
+                We couldn't find a page at this address.
+            </p>
+        </div>
+    </div>
+</div>
+{% endblock %}

web-app/django/VIM/urls.py

@@ -31,3 +31,12 @@
 
 if settings.IS_DEVELOPMENT:
     urlpatterns += [path("__debug__/", include("debug_toolbar.urls"))]
+
+
+###############################################################
+#                     Custom error handlers                   #
+# These handlers define custom views to be displayed for      #
+# specific HTTP error responses.                              #
+###############################################################
+# pylint: disable=invalid-name
+handler404 = "VIM.views.custom_404_page_not_found"

web-app/django/VIM/views.py

@@ -0,0 +1,23 @@
+"""
+Module for custom error views.
+"""
+
+from django.http import HttpRequest, HttpResponse
+from django.shortcuts import render
+
+
+# pylint: disable=unused-argument
+def custom_404_page_not_found(
+    request: HttpRequest, exception: Exception
+) -> HttpResponse:
+    """
+    Custom view to handle 404 errors.
+
+    Args:
+        request (HttpRequest): The request object.
+        exception (Exception): The exception that triggered the 404 error.
+
+    Returns:
+        HttpResponse: Rendered 404 error page.
+    """
+    return render(request, "404.html", status=404)