Adding checks for common URLpattern configuration errors

[Julian Wachholz]

Hi Django-Developers

I would like to add additional system checks to the existing bunch. In
particular, checks regarding common configuration errors around
URLpatterns.

An example check is described in the ticket here:
https://code.djangoproject.com/ticket/23813

Please suggest any other common issues you might have encountered that
would be great to have as a check in the Django core.
And feel free to propose any checks unrelated to URLpatterns, too.

Cheers
Julian