Refactor to better use of classes

[Jake-Pullen]

Pull Request Type: Refactor

1. Title: Removing most of the logic from the database class

2. Description:

• Summary: By moving the logic of the various key parts of the application to their own respective class we will be able to expand quicker and reduce tech debt moving forwards.
• Motivation: Putting all of our core logic into the database class was starting to show cracks, in terms of having a monolithic file instead of organised logic separated files.
• Proposed Solution: By creating classes for each core part of the system we will be able to have a clearer and smoother path to verity development
• Testing: ensured all unit tests pass, added files ready for user and category tests, extensive testing (manually) on firefox.
• Known Limitations/Future Considerations: At this moment, we are still limited only to user and category which is far from done but hopefully this lays the foundation for the rest of the application.

3. Checklist:

[x] I have followed the project's coding style and conventions.
[x] I have written unit tests to cover my changes.
[x] My code has been tested locally.
[x] I have included screenshots/GIFs if applicable.
[x] I have updated the documentation (if necessary).
[x] I have labeled this PR appropriately (e.g., "bug," "feature," "refactor").