Custom user model

[dpgraham4401]

Description

This PR adds a custom user model, HaztrakUser, to the core app as recommended by the django documentation. All apps (beside core) when referencing the user model should reference settings.AUTH_USER_MODEL instead of User from django's Auth module.

We also adjusted the admin site so it does not show DRF Authentication Token model in the admin site. URLs were adjust to point to the new user model, pytest fixtures updated, and foreign keys updated.

Anyone that has previously setup a development environment will need to recreate the necessary docker containers/volume.

Issue ticket number and link

closes #410

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings