Investigate replacements for old backend dependencies

[ssciolla]

As part of my work on PR #207, I noted that these three dependencies in particular seem to be outdated and that we may want to consider replacing them. That said, they all still work with the update to Django 2.2. Possible future work might involve investigating and replacing them.

django-settings-export>=1.2.1,<1.2.99

The last release was in 2016, but it seems to still be used (see Stack Overflow post). That said we could probably write our own context processor to do this, and we only use two settings.py values in templates: LOGIN_URL and CACHE_TTL.

xlrd==1.2.0
xlwt==1.3.0

These two projects last had releases in 2018 and 2017, respectively. They are used primarily for processing Excel files. While the releases aren't too long ago, it seems there might be a more current way of handling this, perhaps using standard libraries. I also noted that xlwt says it is only designed for Excel versions '95 - '03.

[ssciolla]

We discussed this and think that all the libraries are okay for the moment. django-settings-export looks like it has some activity on it, and might see an update in the future; xlrt and xlwd are used by other major libraries likw pandas.

[jonespm]

I'm moving this off this 2.8 project for the moment. This involves replacements rather than just upgrades so should be in a different future issue. Aside from django-settings-export and a few others that aren't mentioned here some of these did have updates. I indicated in the requirements.txt ones I haven't seen updates for.