Database Integration

This branch merges the existing database framework with the card-counting application.

It implements:

1. User account creation that hashes a user's password and creates a User entry in the database.
2. User login by checking that passwords entered in forms match hashed passwords in database.
3. Removes the exposed encryption key in the source code. Assumes the encryption key is now in the ENC_KEY environment variable.
4. Removes tracking of config files
5. Adds a requirements.txt file to manage dependencies