ref(back): Refactor file structure and adds tests

How to test:

Run the backend by using the new command make dev as the Readme says.

Test the backend by running make test file.

To test this with an windows computer, check out Makefile and run the lines individually

Description:

Refactors the backend and adds testing, and adds a new way of running backend.

It is bad practice to have every file open in backend folder and not structured

It restructures the directery structure to look like:

backend/
    - .env
    - .gitignore
    - ...
    - static/
    - prompting/
    - testing/
        - testfiles...
    - app/
        - __init__.py
        - app.py
        - files...

This is needed to finish #22 (closed)