Add custom user model

[helrond]

Is your feature request related to a problem? Please describe.

Zodiac does not have a custom user model. This makes it difficult to extend certain application functionality.

Describe the solution you'd like

Implement a custom user model for Zodiac. Right now, this user can basically give someone the ability to perform write actions in the UI, and everything else can be open to view.

Additional context

This will likely require throwing away the database and starting over, which will be a hassle but not impossible.