Adds pytz as a dependency

[ajrbyers]

When doing a clean install pytz is missing.

  File "/var/www/vermont/src/cms/models.py", line 17, in <module>
    from utils.logic import build_url_for_request
  File "/var/www/vermont/src/utils/logic.py", line 12, in <module>
    from core.middleware import GlobalRequestMiddleware
  File "/var/www/vermont/src/core/middleware.py", line 9, in <module>
    import pytz
ModuleNotFoundError: No module named 'pytz'

It may previously have been loaded automatically but another dependency but now adding it on its own.