Error handling improvements

[ebridges]

Original report by Edward Bridges (Bitbucket: ebridges, GitHub: ebridges).

---

In project/base/urls.py:

# handler400 – See django.conf.urls.handler400.
# handler403 – See django.conf.urls.handler403.
# handler404 – See django.conf.urls.handler404.
# handler500 – See django.conf.urls.handler500.

# e.g.:
# handler400 = 'mysite.views.my_custom_bad_request_view'
# handler403 = 'mysite.views.my_custom_permission_denied_view'
# handler404 = 'mysite.views.my_custom_page_not_found_view'
# handler500 = 'mysite.views.my_custom_error_view'

In project/base/views/errors.py

# CSRF_FAILURE_VIEW
# Default: 'django.views.csrf.csrf_failure'
#
# A dotted path to the view function to be used when an incoming request is rejected by the CSRF protection. The
# function should have this signature:
#
#     def csrf_failure(request, reason=""):
#       ...
#
# where reason is a short message (intended for developers or logging, not for end users) indicating the reason the
# request was rejected. It should return an `HttpResponseForbidden`.
#
# `django.views.csrf.csrf_failure()` accepts an additional `template_name` parameter that defaults to '403_csrf.html'.
# If a template with that name exists, it will be used to render the page.