Demonstrate django-leaflet usage for admin view replacement

[banesullivan]

https://django-leaflet.readthedocs.io/en/latest/index.html this will only work for GDAL tile sources as GDAL is a dependency of django-leaflet

[banesullivan]

After internal discussions, we have decided not to incorporate django-leaflet with django-large-image due to its LGPL license.

While technically (AFAIK), there shouldn't be an issue in using LGPL'd code in a web app like this (because we aren't redistributing the binary), many of our customers are risk averse and would need reassurances after seeing LGPL code in the direct dependencies. This alone is too much of a maintenance burden for us to handle and we'd like the library to grow and be adopted without any concerns from downstream users.

With that said, I think django-leaflet looks like an awesome app, and I may create an implementation (outside of this repo) or example of how to use the two libraries together. I'm going to leave this open and redirect the task as demoing how the two can work together.